Ultra-wideband high data-rate communication apparatus and associated methods

ABSTRACT

An RF transmitter includes a reference signal generator, a signal generator, and a mixer. The reference signal generator provides a reference signal that has a prescribed or desired frequency. The signal generator provides an operating signal in response to a selection signal. The operating signal has a frequency that equals the frequency of the reference signal multiplied by a number. The mixer mixes the operating signal with another signal to generate a transmission signal. An RF receiver includes a first mixer, a second mixer, an integrator/sampler, and a signal generator. The first mixer receives as its inputs an input RF signal and a second input signal, and mixes its input signals to generate a mixed signal. The integrator/sampler receives the mixed signal and processes it to provide an output signal. The signal generator provides an operating signal in response to a selection signal. The operating signal has a frequency equal to the frequency of a reference signal, multiplied by a number. The second mixer mixes the operating signal with a template signal to generate the second input signal of the first mixer.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This patent application is a continuation-in-part of, claimspriority to, and incorporates by reference U.S. patent application Ser.No. 10/206,648, Attorney Docket No. TDCO:015, titled “High Data-RateCommunication Apparatus and Associated Methods,” filed on Jul. 26, 2002.

[0002] Furthermore, this patent application claims priority to, andincorporates by reference, the following patent documents:

[0003] Provisional U.S. Patent Application Serial No. 60/451,538,Attorney Docket No. TDCO:016PZ1, filed on Mar. 3, 2003, and titled“Ultra-Wideband High Data-Rate Communication Apparatus and AssociatedMethods”;

[0004] Provisional U.S. Patent Application Serial No. 60/401,711,Attorney Docket No. Time.166-P, filed on Aug. 7, 2002, and titled “HighData-Rate Communication Apparatus and Associated Methods”; and

[0005] Provisional U.S. Patent Application Serial No. 60/402,677,Attorney Docket No. Time.170-P, filed on Aug. 12, 2002, and titled “HighData-Rate Communication Apparatus and Associated Methods.”

TECHNICAL FIELD

[0006] This patent application relates generally to communicationapparatus and, more particularly, to ultra-wideband (UWB) high data-rate(HDR) communication apparatus.

BACKGROUND

[0007] The proliferation of wireless communication devices in unlicensedspectrum and the ever increasing consumer demands for higher databandwidths has placed a severe strain on those frequency spectrum bands.Examples of the unlicensed bands include the 915 MHz, the 2.4 GHzIndustrial, Scientific and Medical (ISM) band, and the 5 GHz UnlicensedNational Information Infrastructure (UNII) bands. New devices and newstandards emerge continually, for example, the IEEE 802.11b, IEEE802.11a, IEEE 802.15.3, HiperLAN/2 standards. The emergence andacceptance of the standards has placed, and continues to place, afurther burden on those frequency bands. Coexistence among the manysystems competing for radio-frequency (RF) spectrum is taking on anincreasing level of importance as consumer devices proliferate.

[0008] Persons skilled in the art know that the available bandwidth ofthe license-free bands (and the RF spectrum available generally)constrains the available data bandwidth of wireless systems.Furthermore, data-rate throughput capability varies proportionally withavailable bandwidth, but only logarithmically with the availablesignal-to-noise ratio. Hence, to transmit increasingly higher data rateswithin a constrained bandwidth requires the use of complex communicationsystems with sophisticated signal modulation schemes.

[0009] The complex communication systems typically need significantlyincreased signal-to-noise ratios, thus making the higher data ratesystems more fragile and more easily susceptible to interference fromother users of the spectrum and from multipath interference. Theincreased susceptibility to interference aggravates the coexistenceconcerns noted above. Furthermore, regulatory limitations within givenRF bands constrain the maximum available signal-to-noise ratio andtherefore place a limit on the data-rate throughput of the communicationsystem. A need therefore exists for a high data-rate communicationapparatus and system that can readily coexist with other existingwireless communication systems, and yet can robustly support relativelyhigh data-rates in a multipath environment.

SUMMARY

[0010] One aspect of the invention relates to communication apparatus,such as communication transmission apparatus and communication receiverapparatus. In one exemplary embodiment, an RF transmitter according tothe invention includes a reference signal generator, a signal generator,and a mixer.

[0011] The reference signal generator provides a reference signal thathas a prescribed or desired frequency. The signal generator provides anoperating signal in response to a selection signal. The operating signalhas a frequency that equals the frequency of the reference signalmultiplied by a number. More particularly, in some embodiments, thenumber may constitute an integer number, whereas in other embodiments,the number may constitute a non-integer number, as desired. The mixermixes the operating signal with another signal to generate atransmission signal.

[0012] In another exemplary embodiment, an RF receiver according to theinvention includes two mixers, a first mixer and a second mixer. Thereceiver further includes an integrator/sampler and a signal generator.

[0013] The first mixer receives as its inputs an input RF signal and asecond input signal. The first mixer mixes its input signals to generatea mixed signal. The integrator/sampler receives the mixed signal andprocesses it to provide an output signal. The signal generator providesan operating signal in response to a selection signal. The operatingsignal has a frequency equal to the frequency of a reference signal,multiplied by a number. More particularly, in some embodiments, thenumber may constitute an integer number, whereas in other embodiments,the number may constitute a non-integer number, as desired. The secondmixer mixes the operating signal with a template signal to generate thesecond input signal of the first mixer.

BRIEF DESCRIPTION OF THE DRAWINGS

[0014] The appended drawings illustrate only exemplary embodiments ofthe invention and therefore should not be considered as limiting itsscope. The disclosed inventive concepts lend themselves to other equallyeffective embodiments. In the drawings, the same numeral designatorsused in more than one drawing denote the same, similar, or equivalentfunctionality, components, or blocks.

[0015]FIG. 1 shows several power spectral density (PSD) profiles invarious embodiments according to the invention.

[0016]FIG. 2 illustrates exemplary signal waveforms corresponding to ahigh data-rate UWB apparatus.

[0017]FIG. 3 depicts an exemplary embodiment of a high data-rate UWBtransmitter according to the invention.

[0018]FIG. 4 shows exemplary waveforms corresponding to a high data-rateUWB transmitter according to the invention.

[0019]FIG. 5 illustrates an exemplary embodiment of high data-rate UWBreceiver according to the invention.

[0020]FIG. 6 depicts exemplary waveforms corresponding to a highdata-rate UWB receiver according to the invention.

[0021]FIG. 7 shows the timing relationship among various signals in ahigh data-rate UWB transmitter according to the invention.

[0022]FIG. 8 illustrates exemplary desired or prescribed PSD profilesthat correspond to the two modes of operation in illustrativeembodiments according to the invention.

[0023]FIG. 9 shows a PSD profile for an exemplary embodiment of theinvention that uses higher-order harmonics.

[0024]FIG. 10 illustrates an illustrative PSD profile in an exemplaryembodiment according to the invention.

[0025]FIG. 11 shows one cycle of an exemplary output signal of atransmitter in a UWB communication apparatus according to the invention.

[0026]FIG. 11B illustrates one cycle of another exemplary output signalof a transmitter in a UWB communication apparatus according to theinvention.

[0027]FIG. 12 depicts a timing relationship between several signals inan exemplary embodiment according to the invention.

[0028]FIG. 13 shows several PSD profiles for an illustrative embodimentaccording to the invention.

[0029]FIG. 14 illustrates several PSD profiles for other exemplaryembodiments according to the invention.

[0030]FIG. 15 depicts PSD profiles for other illustrative embodimentsaccording to the invention.

[0031]FIG. 16 shows PSD profiles for other exemplary embodiments ofcommunication systems or apparatus according to the invention.

[0032]FIG. 17 illustrates an exemplary embodiment according to theinvention of a communication system that incorporates mode switching.

[0033]FIG. 18 depicts illustrative chipping sequences for use incommunication systems and apparatus according to the invention.

[0034]FIG. 19 shows an exemplary embodiment 19 of a differentialreceiver according to the invention.

[0035]FIG. 20 illustrates a set of offset quadrature phase shift keyed(OQPSK) UWB signals in an exemplary embodiment according to theinvention.

[0036]FIG. 21 depicts a set of chipping signal waveforms in an exemplaryembodiment according to the invention.

[0037]FIG. 22 shows an exemplary embodiment of a transmitter accordingto the invention that uses independently modulated harmonic signals.

[0038]FIG. 23 illustrates an exemplary embodiment of a receiveraccording to the invention for receiving independently modulatedharmonic signals.

[0039]FIG. 24 depicts a sample waveform in an illustrative embodimentaccording to the invention.

[0040]FIG. 25 shows a Fourier transform of the signal in FIG. 24.

[0041]FIG. 26 illustrates sample waveforms in an exemplary embodiment ofa transmitter according to the invention.

[0042]FIG. 27 depicts an exemplary in-phase channel pulse as a functionof time in an illustrative embodiment according to the invention.

[0043]FIG. 28 shows the magnitude of the spectrum of the signal in FIG.27.

[0044]FIG. 29 illustrates an exemplary quadrature channel pulse as afunction of time in an illustrative embodiment according to theinvention.

[0045]FIG. 30 depicts the magnitude of the spectrum of the signal inFIG. 29.

[0046]FIG. 31 shows two signals as a function of time in illustrativeembodiments according to the invention.

[0047]FIG. 32 illustrates the spectra resulting from using the signalshaping shown in FIG. 31.

[0048]FIG. 33 depicts two signals as a function of time in otherillustrative embodiments according to the invention.

[0049]FIG. 34 shows the spectra resulting from using the signal shapingshown in FIG. 33.

DETAILED DESCRIPTION

[0050] This invention contemplates high data-rate communicationapparatus and associated methods. Communication apparatus according tothe invention provide a solution to the problems of coexistingcommunication systems, and yet providing relatively high data-rates.Note that wireless or radio communication systems according to theinvention provide relatively high data-rates in “hostile” propagationenvironments, such as multipath environments. Furthermore, as describedbelow, one may apply the inventive concepts described here to land-linecommunication systems, for example, communication systems using coaxialcables, or the like.

[0051] In one exemplary embodiment according to the invention, a highdata-rate UWB data transmission system uses a binary phase shift keying(BPSK) modulation of a carrier frequency, known to persons of ordinaryskill in the art with the benefit of the description of the invention.One obtains the power spectral density (PSD) at frequency ƒ of such asystem as:${P_{n} = {\frac{2n\quad f_{c}^{2}}{\pi} \cdot {\frac{\sin ( \frac{\pi \quad f}{f_{c}} )}{f^{2} - ( {n\quad f_{c}} )^{2}}}^{2}}},$

[0052] where ƒ_(c) denotes the reference clock frequency, and nrepresents the number of carrier cycles per chip. In other words,$n = {\frac{\# \quad {of}\quad {carrier}\quad {cyles}}{1\quad {chip}}.}$

[0053] A chip refers to a signal element, such as depicted in FIG. 11Aor FIG. 11B. Put another way, a chip refers to a single element in asequence of elements used to generate the transmitted signal. Thetransmitted signal results from multiplying the sequence of chips (thechip sequence) by a spreading code, i.e., the code that spreads thetransmitted signal spread over a relatively wide band. Multiple chips inproportion to a desired energy level per bit encode each data bit.

[0054] In this embodiment, the modulation chipping rate is commensuratewith the carrier frequency. Put another way, n is a relatively smallnumber. In illustrative embodiments, for example, n has a value of lessthan ten, such as 3 or 4. In other illustrative embodiments, one may usen in the range of 1 to 500, or 1 to 42. Using the latter range of valuesof n, one may achieve a UWB bandwidth of 500 MHz or greater, up to afrequency limit of approximately 10.6 GHz, as prescribed in the FederalCommunications Commission's (FCC) Part 15 rules.

[0055] As persons of ordinary skill in the art with the benefit of thedescription of the invention understand, one may use other positiveinteger values of n, as desired. Generally speaking, the choice of thevalues of n depend on one's definition of ultra-wideband. Depending on adesired bandwidth, one may select appropriate values of n, as desired.

[0056] The value of n (rounded up to an integer value) corresponds toapproximately the desired center operating frequency divided by one halfthe desired bandwidth. In other words,${n = \lceil \frac{f_{o}}{\frac{\Delta \quad f}{2}} \rceil},{{{or}\quad n} = \lceil \frac{2f_{o}}{\Delta \quad f} \rceil},$

[0057] where ƒ_(o) and Δƒ denote, respectively, the center operatingfrequency and the desired bandwidth. For instance, the above example ofthe FCC's definition of UWB results in values of n in the range of 1 to42. More specifically, a 500-MHz-wide UWB system operating below (byhalf the bandwidth) the current FCC Part 15 limit frequency of 10.6 GHzresults in:${n = \lceil \frac{10.6 - ( \frac{0.5}{2} )}{( \frac{0.5}{2} )} \rceil},$

[0058] or

n=┌41.4┐=42.

[0059] The FCC has also allowed UWB signals of at least a 500-MHzbandwidth in the frequency range of 22-29 GHz, which corresponds to anupper value of n=116,000. Thus, persons skilled in the art with thebenefit of the description of the invention may choose virtually anyappropriate ranges of values for n, depending on the performance anddesign specifications and requirements for a given application. Notethat generally the signal bandwidth varies inversely with the value ofn.

[0060]FIG. 1 illustrates several PSD profiles for various values of n(the number of carrier cycles per chip). PSD profile 11 corresponds ton=1, whereas PSD profile 12 and PSD profile 13 correspond, respectively,to n=2 and n=3. Note that as the value of n increases, the bandwidth ofthe modulated signal decreases. Note further that, in a UWB system thatone wishes to constrain to a predetermined maximum PSD (e.g., PSDcharacteristics prescribed by a regulatory authority), one seeks toachieve as flat a spectrum as possible in order to maximize the totaltransmitted power in a predetermined bandwidth.

[0061] In such a system, one likewise seeks to choose a transmissionbandwidth independent of the modulation rate in order to maximize thetotal transmitted power. As persons of ordinary skill in the artappreciate, in conventional BPSK systems, the PSD profile is not flateven in the highest bandwidth case, where n=1. Furthermore, thebandwidth depends on the chip rate, as manifested by the parameter n.The dependence of the bandwidth on the parameter n may be undesirablefor a variety of reasons, such as difficulty or failure to meetprescribed regulatory or design specifications.

[0062] For illustrative purposes, FIG. 2 depicts various signalscorresponding to a BPSK transmission system. Carrier signal 21 mayinclude only a fundamental frequency. Alternatively, rather than acontinuous sine-wave signal, carrier signal 21 may include otherwaveforms, as described below. FIG. 2 also shows a pseudo-random noise(PN) sequence 22. Note that the waveforms in FIG. 2 correspond to acommunication system with one chip per RF cycle (i.e., n=1), and 4 chipsper data bit.

[0063] The third waveform in FIG. 2 corresponds to data bits 23.Beginning at time 27 and ending at time 28, PN sequence 22 codes databits 23. The coding of data bits 23 results in signal 24. Signal 24modulates carrier 21 to generate modulated signal 25. Signal 26 acts agating signal. Put another way, the communication system transmitsmodulated signal 25 while the gating signal 26 is active (during theactive portion of signal 26). Modulated signal 25 has a spectrumsubstantially the same as spectrum 11 in FIG. 1 (i.e., the case wherethe parameter n has a value of unity).

[0064] One may determine the data-rate or data throughput of thecommunication system from various system parameters. For example, assumethat the carrier signal has a frequency of 4 GHz, and that the systemoperates with one chip per RF cycle (i.e., n=1) and 4 chips per databit. Given those parameters, persons of ordinary skill in the art whohave the benefit of the description of the invention readily appreciatethat the system provides a 1-gigabit-per-second (Gb/s) data rate.

[0065] One exemplary embodiment of a high data-rate UWB system accordingto the invention includes a high data-rate UWB transmitter and a highdata-rate UWB receiver. FIG. 3 shows an exemplary embodiment of highdata-rate UWB transmitter 4 according to the invention.

[0066] Transmitter 4 includes reference clock 41 (a reference clockgenerator), timing controller 42, data buffer 43, PN generator 45 (apseudo-random noise sequence generator), data/PN combiner 46, mixer 47,antenna 48, and harmonic generator 49. Reference clock 41 generates asignal with a desired frequency. The frequency of reference clock 41corresponds to a carrier frequency for transmitter 4. Thus, thefrequency of reference clock 41 corresponds to the desired carrierfrequency. One may implement reference clock 41 in a number of way andby using various techniques that fall within the knowledge of personsskilled in the art with the benefit of the description of the invention.

[0067] Reference clock 41 couples to harmonic generator 49. Based aclock signal it receives from reference clock 41, harmonic generator 49generates one or more harmonics of the carrier frequency (the frequencyof clock reference 41). For example, given a clock frequency ƒ_(c), asecond harmonic signal at the output of harmonic generator 49 has afrequency 2·ƒ_(c), and so on, as persons skilled in the art with thebenefit of the description of the invention understand. Harmonicgenerator 49 generates the one or more of harmonics synchronously withrespect to the reference clock (i.e., the one or more harmonics aresynchronized to the reference clock).

[0068] Note that one may realize harmonic generator 49 in a number ofways, for example, comb line generators, as persons of ordinary skillwith the benefit of the description of the invention understand. Asanother example, one may use phase-locked loops, as desired. As otherexamples, one may employ an oscillator followed by digital dividercircuitry. By dividing a signal of a given frequency by variousintegers, one may obtain the one or more harmnonics. In connection withsuch an implementation, one may use fractional-N synthesizers, asdesired.

[0069] Furthermore, one may use a variety of circuitry and techniques tosynchronize the one or more harmonics to the reference clock. Suchcircuitry and techniques fall within the knowledge of persons ofordinary skill in the art who have the benefit of the description of theinvention. As an example, a comb line generator may providesynchronization of the one or more harmonics to the reference clock.

[0070] Mixer 47 receives the one or more harmonics from harmonicgenerator 49. Mixer 47 mixes the one or more harmonics of the carrierfrequency with a signal (described further below) that it receives fromdata/PN combiner 46. Mixer 47 provides the resulting signals to antenna48. Antenna 48 propagates those signals into the transmission medium. Inillustrative embodiments, antenna 48 may constitute a wide-band antenna.

[0071] Examples of wide-band antennas include those described in thefollowing patent documents: U.S. Pat. No. 6,091,374; U.S. patentapplication Ser. No. 09/670,792, filed on Sep. 27, 2000; U.S. patentapplication Ser. No. 09/753,244, filed on Jan. 2, 2001; U.S. patentapplication Ser. No. 09/753,243, filed on Jan. 2, 2001; and U.S. patentapplication Ser. No. 09/077,340, filed on Feb. 15, 2002; and U.S. patentapplication Ser. No. 09/419,806, all assigned to the assignee of thepresent application. Furthermore, one may use wide-band horn antennasand ridged horn antennas, as desired. As yet another alternative, onemay employ a differentially driven wire segment as a simple, effective,wide-band radiator. In addition, one may use other suitable wide-bandantennas, as persons of ordinary skill in the art who have the benefitof the description of the invention understand.

[0072] Note that some antennas are of the “constant gain with frequency”types, and result in systems that have frequency dependent propagationcharacteristics. Other antennas, for example, horn antennas, are of the“constant aperture” variety, and produce frequency-independentpropagation behavior. To use harmonics with relatively high frequencies,exemplary embodiments according to the invention use “constant aperturewith frequency” antennas, although one may employ other types ofantenna, as persons of ordinary skill in the art who have the benefit ofthe description of the invention understand.

[0073] Reference clock 41 also couples to timing controller 42. Timingcontroller 42 clocks the data in data buffer 43. Note that timingsignals from timing controller 42 also clock PN generator 45. Databuffer 43 receives its input data from data port 44. A PN sequence fromPN generator 45 modulates the data from data buffer 43 by using data/PNcombiner 46, in a manner that persons of ordinary skill in the art withthe benefit of the description of the invention understand. PN encodeddata from data/PN combiner 46 modulates the one or more harmonics inmixer 47. In illustrative embodiments according to the invention,data/PN combiner 46 constitutes an exclusive-OR (XOR) gate, although onemay use other suitable circuitry, as persons of ordinary skill in theart with the benefit of the description of the invention understand.

[0074] In illustrative embodiments, one may use filters at the output ofharmonic generator 49 to adjust the amplitudes of the one or moreharmonics so that have substantially the same value. Note, however, thatin other embodiments according to the invention, one may use unequalamplitudes, as desired. By using unequal amplitudes, one may control theamount of energy in the transmitted signals at particular frequencies orbands of frequencies.

[0075] Unequal amplitudes affect the amount of energy in various partsof the corresponding PSD profile. For example, reduced (or eliminated)amplitudes result in reduced energy in corresponding frequency bands.(FIG. 16 shows an example of such a system, where one desires to radiateless energy in band 267 so as to improve coexistence with radio systemsoperating within that band.)

[0076]FIG. 4 illustrates exemplary waveforms corresponding to highdata-rate UWB transmitter 4. Signal 421 corresponds to the output ofharmonic generator 49. Signal 422 corresponds to a relatively short PNsequence of 4 chips per data bit. Signal 423 illustrates a relativelyshort data sequence. Signal 429, shown to provide more timing detail fortransmitter 4, constitutes the output signal of reference clock 41.

[0077] Persons of ordinary skill in the art who have the benefit of thedescription of the invention appreciate that, depending on theapplication, chip sequences longer than 4 chips per bit may bedesirable. For example, one may use such chip sequences when thetransmission medium constitutes an RF channel with substantialmultipath, or when one desires more energy per data bit (at the cost ofthe data throughput rate).

[0078] Generally, one may use as few as one chip per bit to obtain themaximum data rate, as desired. Furthermore, one may employ as many astens of thousands of chips per bit in order to obtain “integration” gainat the cost of data rate. Thus, the range for the number of chips perbit may be very broad, as desired, depending on the design andperformance specifications for a particular application, as personsskilled in the art understand. For example, in illustrative embodimentsaccording to the invention, one may generally use 1 to 200 chips perbit, as desired. As another example, in embodiments that comply withIEEE 802.15, one typically desires data rates as high as 480 Mb/s,corresponding to a few chips per bit, and as low as 11 Mb/s, implyingapproximately several hundred chips per bit.

[0079] Persons of ordinary skill in the art who have the benefit of thedescription of the invention appreciate that the number of the PN chipsper data bit is a measure of coding gain useful in mitigating againstinterference and against multipath impairments. Thus, using a largernumber of chips per data bit provides one mechanism for reducing theeffects of interference and multipath.

[0080] As noted above, one may implement data/PN combiner 46 using anexclusive-OR gate. Signal 424 depicts the result of an exclusive-ORoperation on signals 422 and 423. Modulated RF signal 425 results fromcombining signal 421 and signal 424 in mixer 47. Timing signal 426depicts the transmission time for the sequence of data bits 423.

[0081]FIG. 5 illustrates an exemplary embodiment of high data-rate UWBreceiver 5 according to the invention. Receiver 5 includes referenceclock 53, tracking loop 52, integrator/sampler 51, PN generator 55,data/PN combiner 56, mixer 57, antenna 58, and harmonic generator 59.Similarly named blocks and components in receiver 5 may have similarstructure and operation as the corresponding blocks and components intransmitter 4 depicted in FIG. 3.

[0082] Referring to FIG. 5, in high data-rate UWB receiver 5, receivingantenna 58 couples received modulated signal 425 (shown as the signalcoupled to the transmission medium in FIG. 3, with an exemplary waveformdepicted in FIG. 4) to mixer 57. Mixer 57 supplies its output signal tointegrator/sampler 51. Integrator/sampler 51 integrates the outputsignal of mixer 57 to deliver recovered data bit signal 563 as dataoutput 54.

[0083] Mixer 57 also receives template signal 567. Data/PN combiner 56generates template signal 567 from an output of PN generator 55 andharmonic generator 59. In illustrative embodiments according to theinvention, data/PN combiner 56 constitutes an exclusive-OR (XOR) gate,although one may use other suitable circuitry, as persons of ordinaryskill in the art with the benefit of the description of the inventionunderstand. Harmonic generator 59 operates in a similar manner asharmonic generator 49 in FIG. 3, and may have a similar structure orcircuitry.

[0084] A tracking loop 52, well known in the art, controls referenceclock 53 and PN generator 55. Tracking loop 52 controls the timing of PNgenerator 55 for proper signal acquisition and tracking, as persons ofordinary skill in the art with the benefit of the description of theinvention understand. Reference clock 53 provides reference clock signal569 to PN generator 55 and harmonic generator 59.

[0085] Note that one may implement tracking loop 52 in a variety ofways, as desired. The choice of implementation depends on a number offactors, such as design and performance specifications andcharacteristics, as persons skilled in the art understand. Tracking loop52 operates in conjunction with template signal 567 to provide a lockingmechanism for receiving a transmitted signal (template receiver ormatched template receiver), as persons skilled in the art who have thebenefit of the description of the invention understand.

[0086] Mixer 57 mixes the signal received from antenna 58 with templatesignal 567 to generate signal 568. Integrator/sampler 51 integratessignal 568 to generate recovered data signal 563. Integrator/sampler 51drives tracking loop 52, which controls signal acquisition and trackingin high data-rate UWB receiver 5.

[0087]FIG. 6 illustrates exemplary waveforms corresponding to highdata-rate UWB receiver 5. Signal 562 constitutes the output of PNgenerator 55. Signal 561 corresponds to the output of harmonic generator59, whereas signal 567 is the output signal of data/PN combiner. Signal568 constitutes the output signal of mixer 57, which feedsintegrator/sampler 51. Signal 563 is the output signal ofintegrator/sampler 51. Finally, signal 569, shown to provide more timingdetail for receiver 5, constitutes the output signal of reference clock53.

[0088]FIG. 7 shows further details of the timing relationship amongvarious signals in the high data-rate UWB transmitter 4. Waveform 75corresponds to the signals in the transmission medium (i.e., propagatedfrom antenna 48). Waveform 76 shows the transmission periods, i.e.,periods of time during which transmitter 4 transmits. Finally, waveform73 illustrates data bit stream 73 during transmission periods 76.Waveform 79 depicts the clock tick marks for timing reference withrespect to the other waveforms in FIG. 7.

[0089] In other embodiments according to the invention, one may operatehigh data-rate UWB transmitter 4 in either of two modes, depending on aselected or prescribed parameter. Each mode may generate a particular orprescribed PSD profile by using particular or prescribed harmonic orders(i.e., the choice of the harmonics of the carrier to use for each mode).By selecting a particular mode, one may operate transmitter 4 such thatit produced output signals that conform to a particular PSD profile ormeet prescribed conditions (as set forth, for example, by a regulatoryauthority, such as the FCC).

[0090]FIG. 8 depicts two exemplary desired or prescribed PSD profilesthat correspond to the two modes of operation in such embodiments. Atransmitter according to the invention may produce outputs that conformto a selected one of predetermined PSD amplitude profile mask 80 andpredetermined PSD amplitude profile mask 81. In an embodiment of such atransmitter, the frequency of the reference clock (i.e., the frequencyof reference clock 41 in FIG. 3) is approximately 1.8 GHz. Accordingly,the second and third harmonics appear at approximately 3.6 GHz and 5.4GHz, respectively.

[0091] In a first mode of operation conforming to PSD amplitude profilemask 80, one modulates the 3.6 GHz carrier (the second harmonic of thereference clock frequency) with one chip per two RF carrier cycles.Furthermore, one modulates the 5.4 GHz carrier (the third harmonic ofthe reference clock frequency) with one chip per three RF cycles. Inthis mode of operation, the transmitter has a chipping rate of 1.8giga-chips per second. The transmitter produces a transmitted PSDprofile 83. Note that transmitted PSD profile 83 has a substantiallyflat shape, and conforms to PSD mask 80 (i.e., it remains under PSD mask80).

[0092] In a second operating mode, one suppresses the second harmonicwhile modulating the third harmonic 1.80-GHz clock (i.e., the harmonicappearing at 5.6 GHz) at a rate of one chip per four RF cycles. As aresult, the transmitter has a chipping rate of 1.35 giga-chips persecond.

[0093] Note that one may implement embodiments according to theinvention that include more than two operating modes, as desired. Forexample, one may provide a UWB apparatus that includes m operatingmodes, where m denotes an integer larger than unity. One may implementsuch a system in a variety of ways, as persons of ordinary skill in theart with the benefit of the description of the invention understand. Forexample, one may use a bank of selectable harmonic filters (i.e.,selectable choice of which harmonic orders to use) to select anycombination of one or more harmonics. Such a UWB radio apparatus mayselectively avoid interference from or with other radio systemsoperating in the same band or bands. Note that in illustrativeembodiments according to the invention, one may consider “one or more ofm harmnonics” as a form of modulation in addition to the polaritymodulation (i.e., BPSK modulation).

[0094] Although the description above refers to the second and thirdharmonic, persons of ordinary skill in the art who have the benefit ofthe description of the invention appreciate that one may use otherharmonics, as desired. Put another way, in each operating mode, one mayemploy additional harmonics beyond the third harmonic. Using additionalharmonics increases the total transmitted power, while simultaneouslyconforming to the prescribed respective masks (i.e., remaining under thePSD masks).

[0095]FIG. 9 shows a PSD profile for an exemplary embodiment of theinvention that uses higher-order harmonics. Transmitted PSD profile 91corresponds to modulated third and fourth harmonics of a 1.1-GHzreference clock. PSD profile 91 assumes modulation at the rate of 1.1giga-chips per second.

[0096] If one desired more transmitted power, one may employ the thirdthrough seventh harmonics. Doing so results in transmitted PSD profile93. Note that both PSD profile 92 and PSD profile 93 have substantiallyflat shapes. Note further that both PSD profile 92 and PSD profile 93conform to a prescribed or desired PSD amplitude profile mask 90. Thus,by using a number of harmonics of the reference clock frequency thathave an appropriate order, one may implement communication systems withparticular output power profiles that conform to prescribed PSDprofiles, as desired.

[0097] Note that one may use an appropriate clock reference frequencyand associated harmonics to provide co-existence with other devices thatuse a particular RF band or spectrum. For example, in other embodimentsaccording to the invention, the clock reference parameters and theharmonic carriers are selected so that the PSD of the high data rate UWBtransmissions coexist with wireless devices operating in the 2.4 GHz ISMband and in the 5 GHz UNII bands.

[0098] More specifically, in such embodiments, the reference clock has afrequency of approximately 1.1 GHz. Furthermore, the transmitter uses ascarrier frequencies modulated at the reference clock rate ofapproximately 1.1 GHz both the third and fourth harmonics of thereference clock frequency (i.e., 3.3 GHz and 4.4 GHz, respectively).

[0099]FIG. 10 shows an exemplary PSD profile for such an embodiment ofthe invention. Transmission PSD profile 101 fits between the 2.4 GHz ISMband 102 and the 5 GHz UNII bands 103, satisfying a desired level ofcoexistence. Note that the communication system can still support arelatively high data-rate. For example, if one uses 10 PN chips tocomprise one data bit, the resulting data rate is 110 megabits persecond (Mb/s).

[0100] Signal harmonics may be added with a selectable, desired, ordesigned degree of freedom regarding relative phase of the carriers. Forexample, in a communication system according to the invention that usesthe third and fourth harmonics, one may generally represent the timesignals x(t), the sum of the carrier harmonics, by:

x(t)=sin(2π·3·ƒ_(r) t)+sin(2π·4·ƒ_(r) t+φ),

[0101] where ƒ_(r) represents the reference clock frequency and φdenotes a selectable or prescribed phase angle between 0 and 2π radians.Note that in exemplary embodiments according to the invention, one mayrealize the phase angle by using a filter, as persons of ordinary skillin the art with the benefit of the description of the inventionunderstand.

[0102] Note that in exemplary embodiments according to the invention,one may use various values of φ, as desired, where 0≦φ≦2π. FIG. 11Aillustrates one cycle of an exemplary output signal 121A of atransmitter in a UWB communication system according to the invention.Signal 121A corresponds to φ=π. Starting point 122 and ending point 123coincide with the chip boundaries, as illustrated, for example, bysignal 421 and chip signal 422 (output signal of PN generator) in FIG.4.

[0103] Furthermore, note that one may represent output signal x(t) byusing cosines, as desired. In other words,

x _(i)(t)=cos(2π·3·ƒ_(r) t)+cos(2π·4·ƒ_(r) t+φ),

[0104] where ƒ_(r) represents the reference clock frequency and φdenotes a selectable or prescribed phase angle between 0 and 2π radians(inclusive of the end points). FIG. 11B shows one cycle of anotherexemplary output signal 121B of a transmitter in a UWB communicationsystem according to the invention. Output signal 121B has starting point122B and ending point 123B.

[0105] Persons skilled in the art with the benefit of the description ofthe invention appreciate that It will be appreciated that signals x(t)and x_(i)(t) constitute orthogonal signals. One may therefore usesignals x(t) and x_(i)(t) to implement quadrature phase shift keying(QPSK) modulation, as described below.

[0106] Note that signals 121A and 121B have relatively small signallevels at both their starting points (i.e., 122A and 122B, respectively)and their ending points (i.e., 123A and 123B). Exemplary embodimentsaccording to the invention switch signals ON and OFF at those relativelysmall signal levels. Doing so tends to avoid switching transients thatwith imperfect switching might alter the resulting spectrum undesirably.

[0107] In illustrative embodiments according to the invention, one mayrepresent the harmonic carriers by a composite signal S that constitutesa summation of sinusoidal and/or cosinusoidal signals, i.e.,

S(t)=Σ sin{2π·n·ƒ _(r)·(t−s)},

[0108] where the summation extends over the range of harmonics n desired(i.e., it spans the order of the desired harmonics, from the lowest tothe highest). Put another way, the composite signal S constitutes a sumof harmonic carriers over a selected range, n. Note that one may alsoadd cosine harmonics to implement a quadrature UWB communicationapparatus.

[0109] As noted above, in some embodiments, n may range from 3 to 4(corresponding to a UWB communication apparatus operating in a desired3.1 GHz to 5.2 GHz frequency range). FIG. 12 shows the timingrelationship between several signals in such an embodiment according tothe invention, with n=3. Signal 139 depicts a reference clock signal,included to facilitate presentation of the timing relationship betweenthe various signals. Signal 131 corresponds to composite signal S,described above. Signal 132 denotes the sinusoidal signal the harmonicsof which result in composite signal 131. Reference clock signal 139corresponds to the positive-going zero-crossings of sinusoidal signal132.

[0110] Note that time displacement s offsets the chipping signal fromthe carrier signal. More specifically, time displacement s appears as anoffset between reference clock signal 139 (or sinusoidal signal 132) andthe chipping signals.

[0111]FIG. 12 shows signals corresponding to several values of timedisplacement s. Each time displacement s signifies the offset betweenreference clock signal 139 (or sinusoidal signal 132) and one ofchipping signal 133, chipping signal 134, and chipping signal 135,respectively. Specifically, chipping signal 133 corresponds to a timedisplacement s of zero. Chipping signal 134 and chipping signal 135denote, respectively, time displacements of 0.25 and 0.5, respectively.

[0112] Persons of ordinary skill in the art who have the benefit of thedescription of the invention appreciate that, because of symmetry,negative values of s give the same results as positive values of s.Hence, the description of the invention refers to the magnitude of s, or|s|. Also, note that, although FIG. 12 illustrates the chipping sequence“101” as an example for the sake of illustration, persons skilled in theart with the benefit of the description of the invention understand thatone may generally use a desired PN sequence.

[0113]FIG. 13 illustrates several PSD profiles for an illustrativeembodiment according to the invention. PSD profile 143 depicts the powerspectral density of signal 131 multiplied by PN chipping sequence 133.Similarly, PSD profile 144 corresponds to the power spectral density ofsignal 131 multiplied by PN chipping sequence 134. Finally, PSD profile145 illustrates the power spectral density of signal 131 multiplied byPN chipping sequence 135.

[0114]FIG. 13 also illustrates boundary 146 of the 2.4 GHz ISM band andboundary 147 of the UNII band. For two harmonics, a time displacementvalue |s|=0.25 provides a substantially flat PSD profile 144. Persons ofordinary skill in the art who have the benefit of the description of theinvention understand, however, that one may use time displacement values(s) in a range of approximately 0.1 and approximately 0.9 to providesubstantially similar PSD profiles for the third and fourth harmonics,as desired. In a similar manner, one may use other values of timedisplacement s and appropriate numbers of harmonics to implementcommunication systems having desired or prescribed PSD profiles, asdesired.

[0115] As an example, FIG. 14 depicts several PSD profiles thatcorrespond to exemplary embodiments of the invention that use increasingnumbers of harmonics. FIG. 14 includes PSD profile 151, PSD profile 152,and PSD profile 153. A substantially flat PSD profile 151 corresponds toa signal that includes the fundamental frequency through the seventhharmonic, using a time displacement value of |s|=0.375. Similarly, PSDprofile 152 pertains to a signal that includes the second through theseventh harmonics, using a time displacement value of |s|=0.375.Finally, PSD profile 153 corresponds to a signal that includes the thirdthrough the seventh harmonics and uses a time displacement value of|s|=0.375.

[0116] Note that values of time displacement s between approximately 0.1and approximately 0.9 provide substantially flat PSD profiles, similarto the PSD profiles that FIG. 14 illustrates. As noted above, usinglarger numbers of harmonics while conforming to PSD profiles (i.e.,constrained to a maximum PSD value) results in an increase in the totaltransmitted or radiated power.

[0117] One may generate and implement the time displacement s in varietyof ways, as persons of ordinary skill in the art who have the benefit ofthe description of the invention understand. For example, one mayimplement s as digitally derived clock shift in timing controller 42 oftransmitter 4 and PN generator 55 in receiver 4. As another example, onemay implement the desired time shift by using a physical delay line inthe path of the digital input of mixer 47 in transmitter 4 and mixer 57in receiver 5.

[0118] One may obtain the spectra shown in the figures by computing theFourier Transform of the composite signal S. More specifically, wherethe data pulses have a generally rectangular shape and have not beenfiltered (e.g., chipping signal 422 in FIG. 4), one may obtain the PSDas:${{PSD} = {2f_{r}{\int_{0}^{({1/f_{r}})}{\sum\limits_{n = n_{1}}^{n_{2}}\quad {{\sin \lbrack {2{\pi \cdot n \cdot {f_{r}( {t - \frac{s}{f_{r}}} )}}} \rbrack}^{j\quad 2\quad \pi \quad f\quad t}\quad {t}}}}}},$

[0119] where ƒ_(r) denotes the chipping clock frequency, and n₁ and n₂correspond to the order of the harmonics used (i.e., the lower and upperboundaries of the range of harmonics used). Note that one may omitselected harmonics within the range n₁ to n₂ to further shape thespectrum, as desired. FIG. 15 shows an example of applying thistechnique.

[0120] Referring to FIG. 15, PSD profile 161 shows the power spectraldensity for an embodiment of a communication system according to theinvention that uses the third through seventh harmonics of a 1.1-GHzclock. In contrast, PSD profile 162 corresponds to a system that employsthe fifth through the seventh harmonics. As a result, the PSD energy inthe latter system lies mostly above 5 GHz.

[0121] As a third example, PSD profile 163 corresponds to a system thatuses the third, fourth, sixth, and seventh harmonics. Omitting the fifthharmonic in this system results in a gap in the vicinity of 5 GHz to 6GHz. As a result, the system may effectively coexist with systems thatoperate in the 5-GHz UNII band. Note that one may use filtering toreadily remove energy in the side lobes shown in FIG. 15.

[0122] The PSD profiles shown in FIG. 15 correspond to illustrativeembodiments of communication systems according to the invention. Byjudiciously employing selected harmonics together with a chosen clockfrequency, one may design and implement a wide variety of communicationsystems with prescribed PSD profiles in a flexible manner. The choice ofdesign parameters (e.g., clock frequency and the number and order ofharmonics) depend on desired design and performance specifications andfall within the knowledge of persons of ordinary skill in the art whohave the benefit of the description of the invention.

[0123]FIG. 16 shows PSD profiles for other exemplary embodiments ofcommunication systems or apparatus according to the invention. Theseembodiment conform with a PSD mask in which the emissions at 3.1 GHz areat least −10 dB from the peak (marker labeled as 265 in FIG. 16).Furthermore, the mask specifies emissions at 10.6 GHz of at least −10 dBfrom the peak (marker denoted as 266 in FIG. 16).

[0124] UNII band 267 extends from 5.15 GHz to approximately 5.9 GHz.FIG. 16 illustrates four PSD profiles (denoted as profiles 261, 262,263, and 264, respectively) that correspond to different choices of theorder of harmonics used. All four PSD profiles correspond to a basebandchipping reference clock frequency of 1.4 GHz. Furthermore, the PSDprofiles assume time displacement s of approximately 0.375 between thereference clock signal and the chipping sequences (see FIG. 13 andaccompanying description for an explanation of time displacement s andits effect on PSD profiles).

[0125] As noted above, PSD profiles 261, 262, 263, and 264 denotevarious choices of the order of harmonics used. PSD profile 261corresponds to a communication system that uses the 3rd through the 7thharmonics of the chipping reference clock. Thus, such a systemeffectively occupies the allowed bandwidth between 3.1 GHz and 10.6 GHz.

[0126] PSD profile 262 corresponds to a system that employs the 3rd, the5th, the 6th, and the 7th harmonics of the chipping reference clock. Inother words, unlike the system corresponding to PSD profile 261, itomits the fourth harmonic, which overlaps UNII band 267.

[0127] The system corresponding to PSD profile 263 uses the 3rd throughthe 6th harmonics of the chipping reference clock. Thus, this systemomits the relatively higher frequencies by not using higher-orderharmonics.

[0128] PSD profile 264 pertains to a communication system that uses the3rd, the 5th, and the 6th harmonics of the chipping reference clock.This system omits the fourth harmonic, which overlaps UNII band 267. Thesystem may switch its operation modes between PSD profile 261 and PSDprofile 262 or, alternatively, between PSD profile 263 and PSD profile264, as described below in detail.

[0129] Table 1 below summarizes the harmonics used in the systemscorresponding to PSD profiles 261, 262, 263, and 264: TABLE 1 PSDProfile Harmonic Orders Used 261 3, 4, 5, 6, and 7 262 3, 5, 6, and 7263 3, 4, 5, and 6 264 3, 5, and 6

[0130] As noted above, communication systems according to exemplaryembodiments of the invention may include multi-mode operation. Suchsystems may switch from one mode of operation to another mode ofoperation based on desired or prescribed conditions or stimulus.Referring to FIG. 3, controller input signal 40 enables mode switchingin transmitter 4. The state of controller input signal 40, transmitter 4and, more specifically, timing controller 42, determines the chippingduration relative to the reference clock cycle in a manner apparent topersons of ordinary skill in the art who have the benefit of thedescription of the invention.

[0131] Communication systems according to the invention may perform modeswitching in response to virtually any stimulus, as desired. Forexample, a system user may manually selection the mode and thus causemode switching. As an alternative, the mode switching may occur in anautomatic manner, for instance, in response to predetermined or selectedsystem event.

[0132] As another example, the mode switching may occur in asemi-automatic manner, but involve manual user selection in response toan event flagged or brought to the user's attention. In otherembodiments, an internal or external variable or quantity, for example,time, may control mode switching. Alternatively, a remote signalreceived by the communication system may switch the operating mode.

[0133] As yet another example, communications systems and apparatusaccording to various embodiments of the invention may switch modes inresponse to the detection of radio-signal energy in a desired band orbands. For example, in response to detecting the presence ofradio-signal energy in the UNII bands (between 5.15 GHz and 5.85 GHz), aUWB communication apparatus or system according to the invention mayswitch its mode of operation so that its transmissions have a prescribedspectral content. The new mode of operation may correspond to a PSDprofile that tends to eliminate, reduce, or minimize interference withany devices operating in the particular band of interest. For example,the new PSD profile may constitute PSD profile 163 in FIG. 15.

[0134] Thus, the stimulus for the switching of modes in such systems isthe detection of the presence of RF signals from devices operating in aparticular band or at a particular frequency or plurality offrequencies, such as UNII band devices. The response of thecommunication system or apparatus constitutes switching modes so as toeliminate or minimize interference, for example, by omitting theharmonic component that would result in transmitted energy in theaffected frequency range or band. Such a feature provides an additionalmeasure of coexistence with devices operating in existing radiofrequency bands, such as UNII radio devices.

[0135] Note that the above examples constitute only a sampling of howone may switch the operating mode. Depending on desired design andperformance specifications, one may use other techniques and mechanismsfor mode switching, as persons of ordinary skill in the art who have thebenefit of the description of the invention understand. Furthermore, onemay apply any of these techniques to various embodiments ofcommunication systems and apparatus according to the invention, asdesired.

[0136]FIG. 17 shows an exemplary embodiment according to the inventionof a communication system that incorporates mode switching. Highdata-rate UWB communication system 11 includes transceiver 111, whichhas internal power source 112 (e.g., a battery or other power source).System 11 also includes second transceiver 113, with its internal powersource 114 (e.g., a battery or other power source). The mode switchingin system 11 occurs depending on whether the system operates from itsinternal power sources or from an external power source (not shownexplicitly in FIG. 17).

[0137] When system 11 uses internal power source 112 and internal powersource 114, it may operate in a mode that conforms to a particular PSDprofile, for example, PSD mask 81 in FIG. 8. This mode may correspond,for example, to system operation indoors. PSD mask 81, corresponding toindoors operation, may have more relaxed requirements because system 11may cause less potential interference with other systems while itoperates indoors.

[0138] Conversely, when system 11 uses external power (supplied throughport 115 to transceiver 111 and supplied through port 116 to transceiver113), it may operate in another mode that conforms to a different PSDprofile, for example, PSD mask 82 in FIG. 8. The second mode maycorrespond, for example, to system operation outdoors. Thus, byswitching operation modes, WB communication systems according to theinvention can meet more stringent PSD masks outdoors and yet conform toa more relaxed PSD mask while operating indoors.

[0139] To switch modes, system 11 senses the application of externalpower, and supplies a trigger signal to controller input 40 of thetransmitter (see FIG. 3). In response, timing controller 42 and harmonicgenerator 49 adjust pre-determined timing parameters to generate thedesired PSD profile, as described above in reference to FIG. 8. Ananalogous operation occurs in the receiver circuitry of the transceiver.Furthermore, a companion or corresponding transceiver similarly adjustsparameters in its transmitter circuitry and receiver circuitry inresponse to the particular PSD profile that the receiver circuitryreceives.

[0140] Note that, although FIG. 17 shows a pair of transceivers,alternative systems may include a transceiver and a receiver, or atransmitter or receiver, as desired. Mode switching in such systemsoccurs using a similar technique and mechanism as described above, aspersons skilled in the art with the benefit of the description of theinvention understand.

[0141] Another aspect of the invention relates to the shape of thepulses within chipping signal 422 (reproduced in FIG. 18 forconvenience). Chipping signal 422 includes pulses with generallyrectangular shapes. As a consequence, one may generally obtain thespectrum in the frequency domain of the chip as given approximately bythe well-known sinc function, $\frac{\sin \quad (x)}{x}.$

[0142] (A chip corresponds to the distance in time between the verticalsegments of signal 422, or the zero-crossings of signal 222.) Themultiplication operation in mixer 47 shifts that spectrum in thefrequency domain and centers a copy of the spectrum at each of theharmonic signals present in signal 421 (output signal of harmonicgenerator 49).

[0143] Although the description above assumes a chipping signal withpulses that generally have a rectangular shape (e.g., chipping signal422), one may use other pulse shapes, as desired. For example, thepulses may have a more “rounded” shape.

[0144] One example of a more “rounded” pulse shape is the Gaussianimpulse. Mathematically, one may represent a Gaussian impulse s(t) as:${{s(t)} = e^{\frac{{- 0.5}\quad t^{2}}{\tau^{2}}}},$

[0145] where t represents time, and τ denotes a parameter that definesthe pulse width. One may obtain the shape of the spectrum in thefrequency domain by using the Fourier transform of s(t). Mathematically,one may express the Fourier spectrum of s(t) as:

S(ƒ)=e ^(−2(πƒτ)) ² .

[0146] Using the above relationships, one may design a pulse of widthcorresponding to frequency ƒ_(B) (for example 1.1 GHz) where themagnitude of S(ƒ) is below a reference value by a desired amount (forexample, by 10 log[S(ƒ_(B))]=−10 dB). This technique provides a designvalue for τ. which in turn allows one to evaluate s(t).

[0147] Note that FIG. 18 shows a Gaussian impulse as one example. Onemay use other shapes, as desired, as persons of ordinary skill in theart who have the benefit of the description of the invention understand.For example, one may use the trapezoidal shape of chipping signal 133,chipping signal 134, and chipping signal 135 in FIG. 12, as desired.

[0148] Furthermore, note that by shaping or filtering the pulses beforemixing with a signal having a relatively high frequency (a harmonicsignal), one avoids designing or shaping pulses at those relatively highfrequencies. In the case of a filtered signal, one may obtain the PSDfrom:${{PSD} = {2f_{r}{\int_{0}^{({1/f_{r}})}{{p(t)}{\sum\limits_{n = n_{1}}^{n_{2}}\quad {{\sin \lbrack {2{\pi \cdot n \cdot {f_{r}( {t - \frac{s}{f_{r}}} )}}} \rbrack}^{j\quad 2\quad \pi \quad f\quad t}\quad {t}}}}}}},$

[0149] where p(t) denotes the baseband filtered data signal. On exampleis a Gaussian filtered signal, such as one chip of chipping sequence 222in FIG. 18. Also, note that by using multiple harmonics, one may shiftthe shaped pulses in the frequency domain and center the shiftedversions at the desired harmonic carriers.

[0150] Although FIG. 18 shows chipping sequence 422 and chippingsequence 222 as having +1 and −1 amplitude swings, one may use otherswings, as persons of ordinary skill in the art who have the benefit ofthe description of the invention understand. For example, one mayimplement chipping sequences that use +1, 0, and −1 amplitude swings, asdesired.

[0151] One may use various modulation schemes and techniques incommunication systems and apparatus according to the invention, asdesired. For example, exemplary embodiments of the invention may usetechniques analogous to the conventional quadrature phase shift keying(QPSK) systems. Other exemplary embodiments according to the inventionmay use techniques analogous to offset QPSK (OQPSK).

[0152] More particularly, embodiments using QPSK use two harmoniccarriers, which requires two degrees of freedom so that both pairs ofharmonically related signals have a quadrature relationship.Specifically, the phase difference between the two reference clocks andan additional phase delay in one of the harmonic generator lines providethe two desired degrees of freedom. A QPSK-like UWB system according tothe invention with two harmonic carriers has the desired property ofproviding a data rate twice the data rate of a BPSK-like system, whilestill having an essentially flat PSD profile that conforms to prescribedor desired criteria.

[0153] Providing an additional half chip length offset between the twodata streams modulating the quadrature harmonic carriers provides anOQPSK system. Such an OQPSK system has the additional desirable propertyof a smoothed PSD spectrum or profile relative to the PSD profile of theQPSK system.

[0154]FIG. 20 shows one example of the waveforms of an OQPSK UWB signalset in an illustrative embodiment. Signal 2110 comprises sinusoidalharmonics, such as the signal shown in FIG. 11A, while signal 2130comprises cosinusoidal harmonics, like the signal FIG. 11B illustrates.Data stream 2120 modifies the polarity of signal 2110, and data stream2140 modifies the polarity of signal 2130, independent of data signal2120.

[0155] The signal 2130 is furthermore shifted in time to the right ofsignal 2110 so that the maximum envelope value 2135 of signal 2130substantially corresponds with the minimum envelope value 2115 of signal2110. Additionally, to maintain quadrature, the zero-crossings of signal2110 correspond to the respective signal peaks of signal 2130.Conversely, the zero-crossings of signal 2130 correspond to therespective peaks of signal 2110.

[0156] Signal 2150 represents the sum of quadrature signals 2110 and2130. Persons of ordinary skill in the art with the benefit of thedescription of the invention appreciate that the peak-to-average valueof the composite signal is smaller than the peak-to-average values ofeither signal 2110 or signal 2130. This property results in a smootherPSD profile, and enables RF transmissions at a power level that requiresless ‘safety’ margin to the regulatory limit levels.

[0157] In other embodiments according to the invention, one may use adifferential phase shift keying (DPSK) scheme. One may modify atransmitter according to the invention, for example, transmitter 4 inFIG. 3, to generate DPSK signals, as persons of ordinary skill in theart who have the benefit of the description of the invention understand.Transmitter 4 generates DPSK signals as follows. Referring to FIG. 3,transmitter 4 receives data at data input 44. Transmitter 4 encodes thedata differentially, similar to conventional DPSK. More specifically,transmitter 4 encodes the data as changes in the bit stream.

[0158] For example, suppose the sequence starts with a binary “1” bit.If the next bit is a “1,” it indicates that transmitter 4 had sent a “0”previously (no change). On the other hand, if a “0” follows the original“1,” then transmitter 4 encodes a “1.” Thus, transmitter 4 encodeschanges from 1 to −1 (or −1 to 1) as binary “1”s. Conversely,transmitter 4 encodes no bit-to-bit change (e.g., 1 followed by 1, or −1followed by −1) as binary “0”s. As the above description makes evident,to transmit m bits, one transmits m+1 bits (a starting bit, followed bym bits of data), because the changes in the input data bits encode thedata.

[0159] Referring to FIG. 3, data buffer 43 may perform the differentialencoding described above. PN generator 45 generates chip sequencesassociated with a delay or time period D that equals the number of chipsfor a single data bit. The time delay D may be one chip time in oneexemplary embodiment, and may constitute a coded sequence of bits inanother illustrative embodiment (for example, D may be the number ofchips associated with a single data bit). Put another way, one may use aper-chip (time period between starts of two chips) or per-bit (timeperiod between the starts of two bits) time delay D. Regardless of thechoice of time delay D, one keeps D constant for that system.

[0160] In exemplary embodiments according to the invention, one maygenerate chip sequences by using Barker codes or sequences. Each chipsequence is equal in length to one of the known Barker sequences.Preferably, transmitter 4 uses Barker sequences of length 13, 11, or 7,but as persons of ordinary skill in the art who have the benefit of thedescription of the invention understand, one may use other Barkersequences to provide chip sequences, as desired. Table 2 below lists theknown Barker codes: TABLE 2 Length Code Sequence 2 1 −1 or 1 1 3 1 1 −14 1 −1 1 1 or 1 −1 −1 1 5 1 1 1 −1 1 7 1 1 1 −1 −1 1 −1 11 1 1 1 −1 −1−1 1 −1 −1 1 −1 13 1 1 1 1 1 −1 −1 1 1 −1 1 −1 1

[0161] As persons skilled in the art understand, the reverse of the codesequences in Table 2 also constitute Barker codes. Furthermore, theinverse of the listed code sequences (i.e., code sequences obtained byreplacing 1 with −1 and vice-versa) are Barker codes.

[0162] Note that, rather than using Barker codes, one may use othertypes of code, as persons of ordinary skill in the art who have thebenefit of the description of the invention understand. For example, onemay use Kasami codes, as desired. Other examples includes Hadamardcodes, Walsh codes, and codes that have low cross-correlationproperties.

[0163] PN generator 45 multiples each bit obtained from data buffer 43with the Barker sequence. Accordingly, the signal 424 (output signal ofdata/PN combiner 46) constitutes either the Barker sequence or theinverse of a Barker sequence (i.e., obtained by multiplying by −1 thecode sequences in Table 2). Assuming, for example, that PN generatoruses a Barker code of length 11, the time period or delay D equals thelength of 11 chips. As another example, FIG. 12 illustrates one chiptime, which relates to Barker chips in FIG. 6 (signal 562), relating toa Barker code of length 4).

[0164]FIG. 19 illustrates an exemplary embodiment 19 of a differentialreceiver according to the invention that is suitable for receiving DPSKsignals. Receiver 19 includes antenna 910, mixer 916, integrator 918,sample-and-hold 920, and analog-to-digital converter (ADC) 922. Receiver19 may optionally include amplifier 912 and amplifier 914.

[0165] Antenna 910 receives differentially encoded signals. Amplifier912 amplifies the received signal and provides the resulting signal toone input of mixer 916 and amplifier 914. Through delay device 916, theoutput signal of amplifier 916 (if used) couples to another input ofmixer 916.

[0166] The delay D provided by delay device 916 equals one bit time.Accordingly, mixer 916 multiplies the received signal by a version ofthe received signal delayed by a time period D. Because of thedifferential coding of the signals (described above), a bit sign in thedelayed version of the received signal changes when receiver 19 receivesa binary “1.”

[0167] The output of mixer 916 feeds integrator 918. The output of mixer916 constitutes a +1 Barker sequence of Table 2 multiplied by an inverseBarker sequence, thus resulting in a negative going voltage at theoutput of integrator 918 over the length of the Barker code.Sample-and-hold 920 samples the output signal of integrator 918 whenthat signal crosses a threshold. Sample-and-hold 920 provides thesampled signal to ADC 922. ADC 922 provides output data bits.

[0168] Note that, in illustrative embodiments, the length of theintegration may be the time period D. Based on design and performancespecifications, however, one may use longer or shorter time periods, aspersons of ordinary skill in the art who have the benefit of thedescription of the invention understand.

[0169] Optional amplifiers 912 and optional amplifier 914 may constituteeither linear amplifiers or limiting amplifiers, as desired. One mayadditionally use amplifier 914 to compensate for any losses in delaydevice 916. Note that one may place amplifier 912 as shown in FIG. 19or, alternatively, after delay device 916.

[0170] One may implement delay device 916 in a variety of ways, aspersons of ordinary skill in the art who have the benefit of thedescription of the invention understand. For example, a relativelysimple delay device comprises a length of transmission line that haselectrical length D. One may use a length of coaxial line, printedstrip-line, or microstrip in various ways to realize such a device.

[0171] Implementing amplifier 912 and amplifier 914 as limitingamplifiers relaxes the design demands on mixer 916. Mixer 916 may have avariety of structures and circuitry, as persons of ordinary skill in theart who have the benefit of the description of the invention understand.For example, mixer 916 may constitute a passive ring diode mixer or afour-quadrant multiplier, as desired.

[0172] In conventional DPSK systems, the data bits constitute a length Dequal to the length of one data bit. Such systems modulate the phase ofthe carrier (0 or π/2 radians) at the bit rate. In contrast,communication systems or apparatus according to the invention use aBarker encoded sequence of harmonic wavelets (as shown, for example, inFIG. 6) instead of the carrier in conventional systems. Communicationsystems or apparatus according to the invention modulate the polarity ofthe wavelets (i.e., +1 or −1) at the chip rate. Furthermore, theypolarity modulate the chip sequences at the bit rate. Thus, in contrastto conventional DPSK systems, in communication systems and apparatusaccording to the invention, the bit time (see signal 563 in FIG. 6)comprises a coded sequence of wavelets.

[0173] Note that receiver 19 and associated circuitry may performadditional functionality. For example, such circuitry may recover thedata bits, recover timing of the chip sequences, and fine tune theintegration time of integrator 918 in response to signal quality, aspersons of ordinary skill in the art who have the benefit of thedescription of the invention understand.

[0174] Note that the exemplary embodiments described above associateeach data bit with a spreading code of length N. More specifically, onemay use Barker codes of lengths N=2, 3, 4, 5, 7, 11, and 13. Thus, onemay associate N chips with a single data bit. As an example, using aBarker code of length 7 (see Table 2, above), one may transmit a “1” byusing the sequence 1 1 1 −1 −1 1 −1. Similarly, to transmit a “0,” onemay use the sequence −1 −1 −1 1 1 −1 1 (i.e., a sequence obtained bymultiplying by −1 each number in the previous sequence).

[0175] In other embodiments according to the invention, one may usecodes that have a larger length than needed to encode a single bit.Doing so may have several advantages. First, the spectrum of theresulting signal more closely resembles white noise (i.e., the benefitof spectrum “whiteness”).

[0176] Second, one may use such codes to provide channelization. Longercodes have a relatively large number of nearly-orthogonal familymembers. One may use such family members to represent both varioussymbols (i.e., groups of bits) and to provide more effectivechannelization.

[0177] As an example, one may use PN sequence generated which the TIA-95code division multiple access (CDMA). Such a sequence is 32,768 chipslong. One may define channels and symbols by multiplying (e.g., by usingan exclusive-OR operation) the PN sequence (at the chipping rate) with aHadamard code or a Walsh code (i.e., repeated sequences like1111111100000000, 1111000011110000, 1100110011001100, and so on, aspersons skilled in the art understand). Thus, groups of chips areuniquely identify a symbol or channel. Such a techniques takes advantageof a code length of 32,767 to obtain a signal with a relatively smoothspectrum.

[0178] In addition to using relatively long codes to providechannelization, one may use other techniques, such as such astime-division multiplexing and space-division multiplexing (usingdirectional antenna techniques to isolate links), as desired. Suchtechniques fall within the knowledge of persons of ordinary skill in theart who have the benefit of the description of the invention.

[0179] In addition to coding the transmitted data in embodimentsaccording to the invention as described above, one may provideerror-correction coding (ECC), as desired. For example, one may applyECC to data input 44 in FIG. 3, as desired. Many such codes exist in theart, and one may apply them to communication systems and apparatusaccording to the invention as persons skilled in the art with thebenefit of the description of the invention understand. Examples of suchcodes include BCH codes, Reed-Solomon codes, and Hamming codes.

[0180] As noted above, the carrier signal (e.g., carrier signal 21 inFIG. 2) may constitute a sinusoidal or non-sinusoidal carrier signal.FIG. 21 shows examples of some signal waveformns corresponding to anon-sinusoidal carrier signal. FIG. 21 includes a repeating pattern“1010” of chips 2022. Signal 2021 corresponds to the “1010” repeatingpattern of chips. As FIG. 21 illustrates, signal 2021 may have a gap2023 of an arbitrary length (with the parameters of signal 2022, ofcourse) between its segments.

[0181] Another aspect of the invention relates to multiple independentlymodulated harmonic signals (e.g., harmonics of a given frequency, suchas a clock frequency). In other words, in communication apparatusaccording to the invention, one may modulate various harmonic signalswith either the same data stream, or independently, each (or a set) witha different data stream. Thus, the effective data rate constitutes thesum of all the data rates that modulate the harmonic signals.

[0182] Furthermore, one may selectively enable or turn ON each harmonicsignal, as desired. Put another way, one may configure the harmonicsignals independently. In one configuration, the harmonic signals arenot ON or enabled simultaneously. In effect, one may hope from oneharmonic signal or frequency to another harmonic signal or frequency asa function of time, as desired.

[0183] Configuring the harmonic signals by turning them ON selectivelyhas a benefit of simplifying the communication apparatus or system. Thecommunication apparatus or system may operate in the presence ofmultipath interference without a need to resort to coding. Morespecifically, such apparatus or systems may operate in an environmentwhere multipath effects are present without having to code the signalsthat modulate each harmonic signal (as the embodiments described abovedo). Note, of course, that one may still use coding, as desired, but oneneed not do so to combat the effects of multipath interference.

[0184] To combat the effects of multipath interference, communicationapparatus or systems according to the invention transmit one impulse ona given harmonic frequency or channel and then wait for the multipathechoes on that channel to decay before transmitting again. For example,suppose that multipath interference in a given environment has a delayspread of 25 ns. Thus, it takes about 20 ns for the echoes presentbecause of multipath to decay, before one may receive the next impulseor signal (product of the harmonic signal and a signal chip or bit thatcarries one datum bit).

[0185] By using multiple harmonic signals (i.e., two or more harmonics)or frequencies, one may transmit multiple data bits. In other words, onemay transmit a first datum bit on the frequency of a first harmonicsignal, then transmit a second datum bit on the frequency of a secondharmonic signal, and so on, until one transmits the final datum bit(say, datum bit N) using the Nth harmonic signal. One may then repeatthis cycle, as desired.

[0186] The delay between subsequent transmissions using a given harmonicsignal allows the multipath echoes to decay, so that echoes from onetransmission do not interfere with a subsequent transmission that usesthat harmonic signal. In effect, one takes advantage of the fact thatsufficient numbers of the frequency-time combinations exist that beforeone transmits again using a given harmonic frequency, the multipathechoes present at that frequency have decayed sufficiently. Furthermore,by spacing the transmission frequencies sufficiently, one may reduceinterference from multipath echoes of one harmonic frequency withtransmissions on another harmonic frequency.

[0187]FIG. 22 shows an exemplary embodiment of a transmitter 2200according to the invention that uses independently modulated harmonicsignals. Note that dashed lines in FIG. 22 separate circuitry thatoperates at relatively lower frequency from other circuitry thatoperates at relatively high frequency. One may include thelower-frequency circuitry in one IC and include the higher-frequencycircuitry in another IC, as desired.

[0188] Reference clock 41 generates a signal with a desired frequency,for example, a sinewave with a frequency ƒ_(osc). One may implementreference clock 41 in a number of ways and by using various techniquesthat fall within the knowledge of persons skilled in the art with thebenefit of the description of the invention.

[0189] Reference clock 41 couples to harmonic generator 2220. Based aclock signal it receives from reference clock 41, harmonic generator2220 generates an mth harmonic signal of the frequency of clockreference 41. For example, given a clock frequency ƒ_(osc), a secondharmonic signal at the output of harmonic generator 2220 has a frequency2·ƒ_(osc), and so on, such that, generally, the mth harmonic signal hasa frequency m·ƒ_(osc).

[0190] Note that one may vary m during operation of transmitter 2200, asdesired. More specifically, one may vary m per data bit, or on achip-by-chip basis. By varying m, one may generate a desired harmonicsignal that has a given frequency. Thus, by using m=3, one may generatethe third harmonic or, by using m=9, one may generate the ninthharmonic, and so on.

[0191] As persons of ordinary skill in the art who have the benefit ofthe description of the invention understand, one may realize harmonicgenerator 2220 in a number of ways, similar to harmonic generator 49,described above. As one example, one may use a frequency synthesizer. Byvarying the control signal of the frequency synthesizer (e.g., a controlvoltage), one may vary the output frequency of the frequencysynthesizer. Thus, by applying a level of the control signal thatcorresponds to a desired value of m, one may generate the desiredharmonic, as desired.

[0192] Harmonic generator 2220 generates the harmonic signalssynchronously with respect to the reference clock. One may use a varietyof circuitry and techniques to synchronize the one or more harmonics tothe reference clock. Such circuitry and techniques fall within theknowledge of persons of ordinary skill in the art who have the benefitof the description of the invention, as discussed above.

[0193] Transmitter 2200 may also include signal shaping circuitry 2218and mixer 2202. Using signal shaping circuitry 2218 and mixer 2202, onemay shape (or filter) data signals 2206, as desired, and as describedbelow in detail. In embodiments where one uses that option, mixer 2202generates an output signal 2208 that constitutes shaped data pulses.

[0194] Transmitter 2200 also includes mixer 2204 and antenna 48. Outputsignal 2208 feeds one input of mixer 2204. Output signal 2210 ofharmonic generator 2220 feeds another input of mixer 2204. The outputsignal of mixer 2204 constitutes modulated RF signals 2212. Antenna 48accepts modulated RF signals 2212 from mixer 2204 and propagates theminto a transmission medium.

[0195] Note that, by varying the value of m, one may cause transmitter2200 to heterodyne operating frequency of output signal 2208 of mixer2202 (shaped data pulses) to a different RF frequency. In other words,by varying the value of m as a function of time, one may cause theoutput frequency of transmitter 2200 to hop to various frequencies as afunction of time, as described above. One may vary the value of m in avariety of ways, as persons of ordinary skill in the art who have thebenefit of the description of the invention understand. For example, onemay use a controller (not shown explicitly) to control various functionsof transmitter 2200, including selecting the value of m, as desired.

[0196] As persons of ordinary skill in the art with the benefit of thedescription of the invention understand, one may use integer ornon-integer (e.g., fractional) values of m, as desired. Thus, ingeneral, one may derive operating frequency of output signal 2208 ofmixer 2202 by using integer or non-integer values of m, as desired. Putanother way, operating frequency of output signal 2208 of mixer 2202need not (but may) constitute an integer harmonic of the clock signal.Rather, it may relate to the clock frequency in any desired or arbitraryway. For example, the clock frequency may constitute a fraction ofoperating frequency of output signal 2208. Furthermore, one may usefrequency synthesizers, such as fractional-M synthesizers, to generatesuch operating frequencies, as persons of ordinary skill in the art whohave the benefit of the description of the invention understand.

[0197] Furthermore, one may modulate intelligence or information signalsin a variety of ways to generate data signals 2206, as desired. By wayof illustration, one may apply BPSK modulation, quadrature amplitudemodulation (QAM), and QPSK modulation, and the like, as described aboveand understood in the art. The choice of the modulation scheme dependson design and performance specifications for a particularimplementation, as persons of ordinary skill in the art with the benefitof the description of the invention understand.

[0198]FIG. 23 illustrates an exemplary embodiment of a receiver 2300according to the invention for receiving independently modulatedharmonic signals. Receiver 2300 includes antenna 58, mixer 2314, mixer2316, integrator/sampler (integrator/sample-and-hold) 2303, controller2306, baseband template generator 2312, phase-locked loop (PLL) 2319,and harmonic generator 2220.

[0199] Antenna 58 receives RF signals and provides them to one input ofmixer 2314. Output signal of mixer 2316 constitutes a second input ofmixer 2314. Baseband template generator 2312 generates a template signalthat constitutes one input of mixer 2316. The output of harmonicgenerator 2220 constitutes a second input of mixer 2316.

[0200] The output of baseband template generator 2312 matches the outputof signal shaping circuitry 2218 in transmitter 2200 (see FIG. 22).Baseband template generator 2312 generates its output under the controlof PLL 2319. Using feedback within receiver 2300, PLL 2319 generates afirst output signal, reference signal 2322, which it provides tobaseband template generator 2312.

[0201] When receiver 2300 locks onto a desired RF signal, referencesignal 2322 constitutes the same as the reference signal used in thecorresponding transmitter for the RF signal. For example, referring toFIGS. 22 and 23, when receiver 2300 locks onto the signal transmitted bytransmitter 220, reference signal 2322 constitutes a signal similar tothe reference signal that clock reference 41 generates (see FIG. 22). Inother words, PLL 2319 generates reference signal 2322 such that it has afrequency ƒ_(osc).

[0202] PLL 2319 generates a second output signal 2328, which has afrequency ƒ_(osc), that feeds harmonic generator 2220. Harmonicgenerator 2220 operates as described above in connection withtransmitter 2200 in FIG. 22. Thus, harmonic generator 2220 provides aharmonic signal to mixer 2316 that has a frequency m·ƒ_(osc).

[0203] As noted above, the output of mixer 2316 feeds one input of mixer2314. Receiver 2300 uses the output of mixer 2314 to control thefeedback loop that includes PLL 2319 so that the output of mixer 2316matches the RF signals received from antenna 58. The control loopincludes integrator/sampler 2303, controller 2306, and PLL 2319.

[0204] The output of mixer 2314 feeds the input of integrator/sampler2303. Depending on the datum value that receiver 2300 receives,integrator/sampler 2303 provides one of two voltage levels as itsoutput. For example, if receiver 2300 receives a binary zero, the outputof integrator/sampler 2303 may constitute a negative voltage.Conversely, if receiver 2300 receives a binary one, integrator/sampler2303 may provide a positive voltage as its output.

[0205] The output of integrator/sampler 2303 feeds an input ofcontroller 2306. Controller 2306 generates a datum value depending onthe voltage level it receives from integrator/sampler 2303. For example,in response to a positive voltage present at the output ofintegrator/sampler 2303, controller 2306 may generate a binary one bitthat has desired digital level.

[0206] Note that controller 2306 may perform filtering, shaping, and thelike, of the data signals, as desired. Controller 2306 also providesfeedback control signal 2325 to PLL 2319, thus affecting the frequencyof the signals that PLL 2319 generates. Furthermore, controller 2306decides the value of m and provides that value to harmonic generator2220.

[0207] As noted above, harmonic generator 2220 generates as its outputthe mth harmonic of output signal 2328 of PLL 2319. Note that onedetermines the sequence of the values of m as a function of time forboth the receiver and the transmitter. While operating, the receiver andthe transmitter use various values of m according to the predeterminedsequence.

[0208] Note that one may implement the feedback loop within receiver2300 in a variety of ways, as desired. The choice of implementationdepends on a number of factors, such as design and performancespecifications and characteristics, as persons skilled in the art withthe benefit of the description of the invention understand. The feedbackloop uses baseband template generator 2312 to provide a lockingmechanism for receiving a transmitted signal (i.e., a template receiveror matched template receiver), as persons skilled in the art who havethe benefit of the description of the invention understand.

[0209] As noted above, by varying the value of m, communicationapparatus and systems according to the invention may use variousfrequency channels. Furthermore, varying the value of m as a function oftime varies the use of those channels as a function of time. Thus, onemay specify a channel frequency plan and a channel timing plan forcommunication apparatus and systems according to the invention. Byvarying the frequency and channel timing plans, one may design andimplement a wide variety of communication apparatus and system, asdesired.

[0210] Table 3 below shows an example of a channel frequency and timingplan in an illustrative embodiment of a communication apparatus orsystem according to the invention: TABLE 3 M Channels f (GHz) Time Slot(ns) m 1 3.50 24 28 2 3.75 0 30 3 4.00 32 32 4 4.25 8 34 5 4.50 40 36 64.75 16 38

[0211] The example in Table 3 corresponds to a communication apparatusor system that uses six channels. Furthermore, the apparatus or systemuses six time slots, each with an 8 ns duration. Thus, the time slotsrepeat at 48 ns intervals. The harmonics used range from the 28thharmonic to the 38th harmonic. Put another way, m ranges from 28 to 38.With a clock reference frequency of 125 MHz, the channels range infrequency from 3.50 GHz to 4.75 GHz.

[0212] More specifically, at time t=0, m=30 corresponds to a harmonicfrequency of 3.75 GHz. That frequency corresponds to channel 2. Eightnanoseconds later, at t=8 ns, m=34 corresponds to a frequency of 4.25GHz, which corresponds to channel 4, and so on. The frequency shown inthe second column of Table 3 denotes the frequency of the harmonicsignal that is ON or enabled (i.e., modulated and transmitted by thetransmitter).

[0213] Note that one may order the channels and their correspondingfrequencies in a variety of ways, as desired. In an embodiment thatcorresponds to Table 3, one may seek to select the channel frequencycorresponding to a time slot as far apart from neighboring time slotspossible. Referring to Table 3, note that a time period of at least twotime slots (i.e., 16 ns) separates adjacent channels. Selecting thechannel and frequency and timing plan in that manner tends to reduce orminimize interference among the channels, which tends to increase ormaximize channel separation and promote decay of multipath interference.

[0214] Note, however, rather than using the channel plans in Table 3,one may use a wide variety of other apparatus or systems that have othernumbers of channels, frequencies, time slots, and harmonic numbers, asdesired, and as persons of ordinary skill in the art who have thebenefit of the description of the invention understand. Depending on thedesired system performance and design specifications, one may usechannel and frequency and timing plans to improve multipath rejectionperformance and to provide channelization to accommodate multiple usersin a communication system.

[0215] With any given channel frequency and timing plan, one may use avariety of modulation schemes, as desired, and as persons of ordinaryskill in the art who have the benefit of the description of theinvention understand. Examples of modulation schemes include BPSK, QPSK,8-QAM, and 16-QAM. The choice of channels and the type of modulationtechnique used affects the overall data rate of the communication systemor apparatus.

[0216] Table 4 below shows an example of channels used and theapproximate resulting data rates of throughput (in megabits per second)for various modulation techniques: TABLE 4 No. of Channels Used BPSKQPSK 8-QAM 16-QAM 1 20.8 41.7 83.3 166.7 2 41.7 83.3 166.7 333.3 3 62.5125.0 250.0 500.0 4 83.3 166.7 333.3 666.7 5 104.7 208.3 416.7 833.3 6125.0 250.0 500.0 1000.0 Est. E_(b)/N_(o) (db) 7 7.5 12 16

[0217] Note that, rather than using six channels as Table 4 shows, onemay use fewer or more channels, as desired. The choice of the number ofchannels and the modulation technique used depends on factors such assystem performance and design specifications and considerations, aspersons skilled in the art with the benefit of the description of theinvention understand.

[0218] Furthermore, Table 4 corresponds to a UWB system with anapproximately 500 MHz bandwidth per channel. One may apply the inventiveconcepts to a variety of UWB systems with other bandwidths, as desired.The bandwidth of 500 MHz corresponds to the smallest bandwidth definedas UWB in 47 C.F.R. Part 15 of the FCC rules and regulations.

[0219] Note further that Table 4 corresponds to a system with a pulserepetition rate of approximate 20.83 MHz. This pulse repetition ratecorresponds to 8 nanosecond long pulses (one cycle of the 125 MHzreference) sent every 48 nanoseconds at a {fraction (1/48)} ns(approximately 20.83 MHz) pulse repetition rate.

[0220] The last row in Table 4, labeled “Est. E_(b)/N₀ (dB),” denotesthe estimated or approximate energy used for each transmitted bit in thepresence of noise. Referring to Table 4, of the modulation schemeslisted, that BPSK modulation has the lowest amount of energy per bit tonoise density ratio (7 dB for an approximate 0.1% bit error rate), butalso has the lowest overall data throughput. Conversely, 16-QAM has thehighest energy per bit to noise density ratio (16 dB for anapproximately 0.1% bite error rate), but has the highest overall datathroughput (roughly eight times higher than BPSK). Generally, the morecomplex a modulation scheme, the higher the energy level it uses totransmit a bit with a specified bit error rate in the presence of noise.

[0221] One may use the information from Table 4 to design and implementcommunication apparatus or systems that may meet the IEEE 802.15.3aproposed draft standard. The proposed draft specifies data rates ofabout 110 megabits per second, about 200 megabits per second, and about480 megabits per second. The cells highlighted with bold numbers inTable 4 show combinations of modulation schemes and numbers of channelsthat one may use to implement such apparatus or systems in a flexiblemanner.

[0222] Such flexibility is desirable because with the regulatorytransmissions limits specified as power spectral density limits, thetotal transmission power is proportional the total bandwidth used (inother words on the number of channels used in Table 4). Thus, one maytransmit 125 Mb/s in three channels by using QPSK or, alternatively, insix channels by using BPSK. With six channels the total radiated powermay be twice that of three channels for extended range communications.Hence, in a system, one may trade bandwidth for range at a given ordesired data rate.

[0223] One aspect of apparatus or systems according to the inventionconcerns their scalability. More specifically, one may design aplurality of 500 MHz-wide channels in the frequency range of 3.1 to 5.2GHz, using ƒ_(osc) of 125 MHz, with the following center frequencies:

ƒ₁=28ƒ_(osc)=3.500 GHz,

ƒ₂=29ƒ_(osc)=3.625 GHz,

ƒ₃=30ƒ_(osc)=3.750 GHz,

. . .

and

ƒ₁₃=40ƒ_(osc)=5.000 GHz.

[0224] In a rulemaking, the FCC has limited UWB emissions to −41.3 dBmper MHz. For each channel, one may determine the power from thefollowing equation:

P _(c)=−41.3+10 log(2.374ƒ_(osc))

[0225] or −16.6 dBm per channel.

[0226] Thus, increasing the number of channels to provide higher datarates also increases the total emitted power. For example, 2 channelswould provide 3 dB more power than a single channel. As another example,4 channels would provide 6 dB more power than a single channel, and soon. Using multiple channels increases the total emitted power by thesame ratio as it increases the overall data rate or data throughput ifone uses a single modulation scheme (e.g., not switching from BPSK toQPSK, and so on).

[0227] Consequently, the communication range remains approximatelyconstant with an increase in the data rate or data throughput or, asstated above, one may trade bandwidth for communications range. Thus,apparatus or systems according to the invention provide a desirablescalability feature such that increasing the data rate or datathroughput does not decrease the communication range. In other words,one may achieve communication with a higher data throughput at a desiredrange by increasing the number of channels and, hence, increasing thetotal emitted power.

[0228] Note that the examples described above with particular systemparameters, such as frequencies and frequency ranges, constituteillustrative embodiments of the inventive concepts. As persons ofordinary skill in the art with the benefit of the description of theinvention understand, one may use a variety of other system parameters(e.g., frequencies and frequency ranges), as desired, depending onvarious factors, such as desired design and performance specifications.

[0229] As an example, one may use two channels in the 3.1 to 5.1 GHzband, with ƒ_(osc)=232 MHz (i.e., the channels are wider than 500 MHz),with the following center frequencies:

ƒ₁=16ƒ_(osc)=3.712 GHz, and

ƒ₂=20ƒ_(osc)=4.640 GHz,

[0230] or m=16 and 20, respectively, and where

P _(c)=−41.3+10 log(2.374ƒ_(osc)),

[0231] or −13.9 dBm.

[0232] By ruling, the FCC has allowed UWB emissions in the 3.1 to 10.6GHz frequency band or range. The exemplary channel plans describedconform to the FCC rules while allowing co-existing communications withthe UNII band. Thus, the 3.1 to approximately 5.2 GHz range constitutesan example of a desirable frequency range if one wishes to avoidpossible interference with communications in the UNII band.

[0233] The FCC rulemaking referenced above specifies one mask with abandwidth defined at −10 dB points. In the example given above, the −10dB point occurs at 2ƒ_(osc)=464 MHz, while the −20 dB point occurs at2.62ƒ_(osc)=607.84 MHz. Thus, an apparatus or system according to anillustrative embodiment based on this example meets that FCCspecification of −10 dB at 3.1 GHz. Note that, in this example, the twocenter frequencies correspond to a bandwidth of 928 MHz, and that twochannels fit in the desired frequency range, here between 3.1 and 5.2GHz.

[0234] Of course, one may implement other embodiments according to theinvention with a wide variety of parameters, such as frequency plans,modulation schemes, and the like, as persons skilled in the art with thebenefit of the description of the invention understand. In fact, one mayuse other frequency synthesis methods in which the value of m does notconstitute an integer, as noted above.

[0235] Another aspect of the invention relates to signal shaping incommunication apparatus. More specifically, signal shaping circuitry2218 in FIG. 22 provides a way of shaping, processing or filteringoutput signal 2202A of reference clock 41 to generate shaped outputsignal 2204A. Shaped output signal 2204A feeds one input of mixer 2202,as described above.

[0236] The signal shaping circuitry 2218 affects the spectrum of outputsignal of mixer 2204, which essentially constitutes the transmittedsignal of transmitter 2200. More specifically, rather than using signalshaping circuitry 2218 to mix shaped signal 2204A with data signals2206, one may merely provide data signals 2206 to mixer 2204. As aconsequence of bypassing or not using signal shaping circuitry 2218, thespectrum of the transmitted signal includes relatively high side lobelevels. Those side lobe levels may fail to fit a desired mask, such as amask that the FCC or another regulatory body has prescribed.

[0237] By using signal shaping circuitry 2218, one may reduce or lowerthe side lobes of the transmitted signal. Consequently, the spectrum ofthe transmitted signal tends to more easily meet more stringent spectralradiation or mask requirements. Note that one applies an analogoussignal shaping function in a receiver that receives and processessignals transmitted by transmitter 2200.

[0238] Referring to FIG. 23, receiver 2300 constitutes a matchedtemplate or matched filter receiver. Baseband template generator 2312provides the same or analogous signal shaping functionality as doessignal shaping circuitry 2218 in transmitter 2200. In other words, asnoted above, the output of baseband template generator 2312 matches theoutput of signal shaping circuitry 2218 in transmitter 2200.

[0239] Note that signal shaping circuitry 2218 (and the correspondingsignal shaping in receiver 2300) may provide virtually any desiredsignal shaping, processing, or filtering function, as desired. By way ofillustration, signal shaping circuitry 2218 may add a DC component (suchas a DC voltage), it may provide a magnitude function (e.g., byperforming full-wave rectification of the input signal), and the like,as persons skilled in the art who have the benefit of the description ofthe invention understand.

[0240] Furthermore, one may combine various functions together, asdesired. For example, one may add a DC offset to a magnitude function.Generally, one may apply a wide variety of signal shaping functions orcombinations of functions by configuring the transfer function of signalshaping circuitry 2218. The choice of the function(s) to use depends ona variety of design and performance factors, such as desired spectralcharacteristics and/or desired levels of out of band energy, and thelike, as persons of ordinary skill in the art who have the benefit ofthe description of the invention understand.

[0241] Rather than using analog circuitry to shape signals, one may usedigital circuitry or a mixed-mode circuitry, as desired. For example,one may store signal samples in a memory, such as a read-only memory(ROM), and based on the input signal to signal shaping circuitry 2218,use a counter to access various addresses in the memory in other togenerate a desired signal at the output of signal shaping circuitry2218.

[0242] By using an appropriate transfer function for signal shapingcircuitry 2218, one may smooth the spectrum of data signals 2206 or, putanother way, reduce the high frequency content of baseband data signals2206. As noted above, data signals 2206 generally have pulse shapes(e.g., a square-wave or pulse train). Suppose, for example, that signalshaping circuitry 2218 applies a magnitude function to output signal2202A of reference clock 41.

[0243] Output signal 2204A of signal shaping circuitry 2218 constitutesa rectified cosine signal, and its spectrum contains less high-frequencycontent than does the spectrum of data signals 2206. Accordingly, outputsignal 2212 of mixer 2204 and, hence, the transmitted signal, has sidelobes with lower levels.

[0244] In the above example, note that one may implement the magnitudefunction without using analog filtering components, as persons skilledin the art with the benefit of the description of the inventionunderstand. Thus, one may implement the magnitude function in an IC thatcontains primarily digital circuitry, as desired. Doing so provides moreprocessing and manufacturing flexibility, which may result in higherreliability and lower cost.

[0245]FIGS. 24 and 25 show sample waveforms for one example of amagnitude function realized in an illustrative embodiment of a pulseshaping circuitry 2218 according to the invention. More specifically,FIG. 24 illustrates one cycle of output signal 2208 of mixer 2202 inFIG. 22 (assuming rectangular data signals 2206). In other words,reference clock 41 generates a cosine signal that it provides to signalshaping circuitry 2218. Signal shaping circuitry 2218 processes thatsignal to generate its magnitude, and provides the resulting signal(signal 2204A) to mixer 2202. Mixer 2202 mixes signal 2204A with inputdata signals 2206 to generate output signal 2208.

[0246]FIG. 25 depicts a Fourier transform of the signal in FIG. 24. Putanother way, FIGS. 24 and 25 provide time and frequency domainrepresentations, respectively, of output signal 2208 of mixer 2202.Thus, the waveform in FIG. 24 depicts the time signal:

s(t)=cos(2πƒ_(osc) t),

[0247] and the spectrum in FIG. 25 illustrates the spectrum of s(t), orS(ƒ):${S(f)} = {\frac{f_{osc}^{2}{\cos ( \frac{\pi \quad f}{2f_{osc}} )}}{( {f_{osc}^{2} - f^{2}} )}.}$

[0248] In this exemplary embodiment, signal shaping circuitry 2218realizes a magnitude function. The magnitude of the cosine function(i.e., output signal 2204A of signal shaping circuitry 2218), multipliedby the input data signals 2206, generates output signal 2208 of mixer2202, as FIG. 24 illustrates (note, however, that FIG. 24 shows onecycle of signal 2208). As noted above, FIG. 25 illustrates the Fouriertransform of the signal in FIG. 24. Effectively, in such animplementation, the input chip is weighted by a cosine function.

[0249] Note that the maximum chip rate constitutes twice the frequencyof the reference clock, or 2ƒ_(osc). One may, however, send sparse chipsat a rate of: ${R = \frac{2f_{osc}}{N}},$

[0250] where 0≦N≦┌2ƒ_(osc)┐. Furthermore,

P _(c)=−41.3+10 log(2.374ƒ_(osc)),

[0251] and the −10 dB point and the −20 dB point constitute,respectively, 2ƒ_(osc) and 2.62ƒ_(osc). One may write the closestfrequency above 3.1 GHz (the edge of the FCC-prescribed mask) where thesignal level is −20 dB (or less), ƒ₁, as:

ƒ₁=(m−2.62)·ƒ_(osc),

[0252] where m constitutes an integer.

[0253] Note that the signal in FIG. 24 and its associated spectrum inFIG. 25 constitute baseband signals. In other words, the spectrum of thesignal in FIG. 24 centers around zero frequency, or DC. As thetransmitter in FIG. 22 shows, one may heterodyne the baseband signal soas to center it around a relatively high frequency (an RF frequency).More specifically, one may use mixer 2204 to heterodyne output signal2208 of mixer 2202 (by mixing it with signal 2210) and center it arounda frequency m·ƒ_(osc).

[0254] The heterodyning process shifts the spectrum of signal 2208 to afrequency band. The frequency band may constitute a desired frequencyband, such as a band prescribed by a regulatory body (e.g., the FCC), orany other prescribed, specified, or designed frequency band. Using theinventive concepts described here, one may design an RF apparatus orsystem such that the shifted spectrum fits or satisfies a desired orprescribed mask, for example, a mask specified in the FCC's rulemaking.

[0255]FIG. 26 illustrates sample waveforms in an exemplary embodiment ofa transmitter according to the invention, such as transmitter 2200 inFIG. 22. Waveform 2605 corresponds to output signal 2202A of referenceclock 41. Waveform 2610 denotes shaped output signal 2204A, i.e., theoutput of signal shaping circuitry 2218. In this particular embodiment,shaped output signal 2204A constitutes the magnitude of signal 2202A. Asnoted above, however, one may configure signal shaping circuitry 2218 torealize virtually any signal shaping or transfer function, as desired.

[0256] Waveform 2615 depicts input data signals 2206 (see FIG. 22).Waveform 2620 illustrates output signal 2208 as a function of time,i.e., the output signal of mixer 2202. Note that, as described above,waveform 2620 corresponds to the product (by mixing) of waveform 2610and waveform 2615. As noted above, waveform 2620 corresponds to abaseband signal (i.e., a signal centered around zero frequency, or DC).

[0257] Waveform 2625 denotes output signal 2210 of harmonic generator2220. Note that waveform 2625 corresponds to a particular value of m. Asnoted above, the value of m varies as a function of time. Thus, thefrequency of waveform 2625 also varies as a function of time (inproportion with the value of m).

[0258] Waveform 2630 illustrates the output signal of mixer 2204, whichconstitutes modulated RF signals 2212. Note that mixer 2204 mixes outputsignal 2208 (a baseband signal) with output signal 2210 of harmonicgenerator 2220 (an RF signal) to generate modulated RF signals 2212.

[0259] As persons of ordinary skill in the art with the benefit of thedescription of the invention understand, one may generate in-phase andquadrature orthogonal channels as part of the heterodyning scheme. Morespecifically, by mixing output signal 2208, or a pulse, with a cosinesignal, one may generate an in-phase or I channel. Thus,

s ₁(t)=[cos(2πƒ_(osc) t)]·cos(2πƒ_(o) t),

[0260] and${{S(f)} = {f_{osc}^{2} \cdot {\frac{\cos ( \frac{\pi\lbrack {{f} - f_{0}} \rbrack}{2f_{osc}} )}{( {f_{osc}^{2} - \lbrack {{f} - f_{0}} \rbrack^{2}} )}}}},$

[0261] where

ƒ_(o) =m·ƒ _(osc)·

[0262]FIG. 27 illustrates an exemplary I-channel pulse (as mixed togenerate a shifted or heterodyned signal) as a function of time. FIG. 28shows the magnitude of the spectrum of the signal in FIG. 27. Note thatheterodyning has shifted the spectrum of the baseband signal and hascentered it around a relatively high frequency (approximately 4 GHz).

[0263] Conversely, mixing output signal 2208, or a pulse, with asinusoid, one may generate a quadrature or Q channel. Thus,

s _(Q)(t)=[cos(2πƒ_(osc) t)]·sin(2πƒ_(o) t),

[0264] and${S(f)} = {f_{osc}^{2} \cdot {{\frac{\cos ( \frac{\pi\lbrack {{f} - f_{0}} \rbrack}{2f_{osc}} )}{( {f_{osc}^{2} - \lbrack {{f} - f_{0}} \rbrack^{2}} )}}.}}$

[0265]FIG. 29 illustrates an exemplary Q-channel pulse (as mixed togenerate a shifted or heterodyned signal) as a function of time. FIG. 30shows the magnitude of the spectrum of the signal in FIG. 29. Note thatheterodyning has shifted the spectrum and has centered it around arelatively high frequency (approximately 4 GHz).

[0266] Note further that the formulae for S(ƒ) for the I and Q channels,and the magnitude of the spectra in FIGS. 28 and 30, are the same. Aspersons skilled in the art with the benefit of the description of theinvention understand, the phase of the spectra are different for the Iand Q channels. (As noted above, however, FIGS. 28 and 30 depict themagnitude of the respective spectra and therefore do not illustrate thephase differences.)

[0267] As noted above, by using signal shaping circuitry 2218, one mayreduce the magnitude of the side lobes present in the output spectra orprofiles of transmitter 2200 (see FIG. 22). FIGS. 31 and 32 illustrateexamples of how shaping the pulses affects the side lobe magnitudes.

[0268]FIG. 31 shows two signals as a function of time that correspond toa cosine-shaped pulse and a pulse with no shaping, in illustrativeembodiments according to the invention. Signal 3105 corresponds to acosine-shaped pulse in output signal 2212 (see FIG. 22) or, putdifferently, to a situation where one realizes a magnitude function byusing signal shaping circuitry 2218. Signal 3110, on the other hand,corresponds to a situation where one does not apply any signal shapingto signal 2202A. In other words, in the latter situation, signal 2204Aconstitutes a rectangular pulse or a DC level.

[0269]FIG. 32 illustrates the spectra resulting from using the signalshaping shown in FIG. 31. Spectrum 3205 corresponds to thecosine-weighted pulse (shown as signal 3105 in FIG. 31). Spectrum 3210corresponds to the situation where one does not apply any signalshaping. Note that the side lobes of spectrum 3205 have a smallermagnitude than do the side lobes of spectrum 3210. Spectral mask 3215denotes a desired or specified mask, such as a mask prescribed by theFCC.

[0270] As noted above, one may apply virtually any signal shaping viasignal shaping circuitry 2218. FIGS. 33 and 34 provide additionalexamples of how shaping the pulses affects the side lobe magnitudes.

[0271]FIG. 33 shows two signals as a function of time that correspond toa Gaussian-shaped pulse and a pulse with no shaping, in illustrativeembodiments according to the invention. Signal 3105 corresponds to aGaussian-shaped pulse in output signal 2212 (see FIG. 22) or, putdifferently, to a situation where signal shaping circuitry 2218generates a Gaussian-shaped signal (or an approximation to aGaussian-shaped signal), as described by the equation s(t)=e^(−0.5t) ²^(/τ) ² , at its output. Signal 3110, similar to FIG. 31, corresponds toa situation where one does not apply any signal shaping to signal 2202A.

[0272]FIG. 34 illustrates the spectra resulting from using the signalshaping shown in FIG. 33. Spectrum 3405 corresponds to theGaussian-weighted pulse (shown as signal 3305 in FIG. 33). Spectrum 3410corresponds to the situation where one does not apply any signalshaping. Similar to FIG. 32, note that the side lobes of spectrum 3405have a smaller magnitude than do the side lobes of spectrum 3410.Spectral mask 3415, similar to spectral mask 3215 in FIG. 32, denotes adesired or specified mask, such as a mask prescribed by the FCC.

[0273] Note that the choice of signal shaping function realized orapplied by signal shaping circuitry 2218 tends to not affect thecharacteristics of the main lobe in the spectrum of the resulting outputsignal of the transmitter. In other words, although certain signalshaping schemes (for example, the techniques described above) tends toreduce the magnitude of the spectral side lobes, the main lobecharacteristics tend to remain relatively unaltered. As an example, notethat in FIG. 32, the main lobe in spectrum 3205 has a substantiallysimilar shape and magnitude as does the main lobe in spectrum 3210.

[0274] Depending on the signal shaping implemented or realized by signalshaping circuitry 2218, the side lobes in the spectrum of the resultingsignal at the output of mixer 2202 (i.e., signal 2212 in FIG. 22) mayhave too high a magnitude. In other words, the side lobes in thespectrum of the resulting signal may exceed a limitation prescribed by aparticular mask. In such cases, one may filter signal 2212 beforeproviding it to antenna 48. One may configure or design the transferfunction (i.e., the filtering characteristics) of the filter to removeor reduce energy at certain frequencies or within certain frequencybands. Doing so reduces the side lobe magnitudes that would otherwisenot fit within the constraints of the particular mask.

[0275] Apparatus and methods according to the invention are flexible andlend themselves to a broad range of implementations, as persons ofordinary skill in the art who have the benefit of the description of theinvention understand. One may design, implement, and manufacturecommunication apparatus and systems according to the invention using awide variety of semiconductor materials and technologies. For example,one may use silicon, thin-film technology, silicon-on-insulator (SOI),silicon-germanium (SiGe), gallium-arsenide (GaAs), as desired.

[0276] Furthermore, one may implement such systems and apparatus usingn-type metal oxide semiconductor (NMOS), p-type metal oxidesemiconductor (PMOS), complementary metal oxide semiconductor (CMOS),bipolar junction transistors (BJTs), a combination of BJTs and CMOScircuitry (BiCMOS), hetero-junction transistors, and the like, asdesired. The choice of semiconductor material, technology, and designmethodology depends on design and performance specifications for aparticular application, as persons of ordinary skill in the art who havethe benefit of the description of the invention understand.

[0277] Note that, by taking advantage of standard semiconductor devicesand fabrication technology, one may manufacture communication systemsand apparatus according to the invention with high yield, highreliability, and low cost. For example, one may manufacture such systemsand apparatus using standard mixed-signal CMOS processes. Thisflexibility allows manufacture and marketing of high data-rate consumerproducts, professional products, health-care products, industrialproducts, scientific instrumentation, military gear, and the like, thatemploy communication systems and apparatus according to the invention.

[0278] Although the above description of communication systems andapparatus relates to wireless communications, one may use the disclosedinventive concepts in other contexts, as persons of ordinary skill inthe art who have the benefit of the description of the inventionunderstand. For example, one may realize high data-rate land-line (i.e.,using cables, fiber optics, house wiring, coaxial lines, twin-leadlines, telephone lines, cable television lines, and the like)communication systems and apparatus, as desired.

[0279] Put another way, one may omit the antennas (and any associatedcircuitry) and couple the transmitter and receiver together via atransmission line such as a wire line or an optical fiber. In suchsystems, one obtains the same or similar benefits as the wirelesscounterparts. More specifically, the UWB signal can coexist with othersignals on the same transmission medium.

[0280] The spectra shown in various figures (e.g., FIGS. 13-16) arerepresentative of transmitted and emitted spectra. Radio wavepropagation in free space exhibits no frequency dependency, so the fieldstrength PSD at the receiver is the same as the transmitted PSD, and thesignal attenuates as 1/(4πr ²). As noted above, if one receives thesignal with a constant-aperture type of antenna, then the receivedspectrum equals the transmitted spectrum. An example of aconstant-aperture antenna is a wide-band horn or a wide-band parabolawhose gain increases as the square of frequency.

[0281] On the other hand, if one receives the signal with aconstant-gain type of antenna, then the received spectrum will have animposed 1/ƒ² characteristic. An example of a suitable constant-gainantenna is a wide dipole whose gain is essentially flat with frequency.Non-free-space environments may exhibit some frequency dependencies.Those effects, however, are essentially equal whether one employs aconstant-aperture or a constant-gain antenna is employed.

[0282] Referring to the figures, the various blocks shown (for example,FIG. 3 or FIG. 5) depict mainly the conceptual functions and signalflow. The actual circuit implementation may or may not containseparately identifiable hardware for the various functional blocks. Forexample, one may combine the functionality of various blocks into onecircuit block, as desired. Furthermore, one may realize thefunctionality of a single block in several circuit blocks, as desired.The choice of circuit implementation depends on various factors, such asparticular design and performance specifications for a givenimplementation, as persons of ordinary skill in the art who have readthe disclosure of the invention will understand.

[0283] Other modifications and alternative embodiments of the inventionin addition to those described here will be apparent to persons ofordinary skill in the art who have the benefit of the description of theinvention. Accordingly, this description teaches those skilled in theart the manner of carrying out the invention and are to be construed asillustrative only.

[0284] The forms of the invention shown and described should be taken asthe presently preferred embodiments. Persons skilled in the art may makevarious changes in the shape, size and arrangement of parts withoutdeparting from the scope of the invention described in this document.For example, persons skilled in the art may substitute equivalentelements for the elements illustrated and described here. Moreover,persons skilled in the art who have the benefit of this description ofthe invention may use certain features of the invention independently ofthe use of other features, without departing from the scope of theinvention.

I claim:
 1. A radio-frequency (RF) transmitter, comprising: a referencesignal generator, the reference signal generator configured to provide areference signal having a frequency; a signal generator, the signalgenerator configured to provide an operating signal in response to aselection signal, wherein the operating signal has a frequency equal tothe frequency of the reference signal multiplied by a number; and afirst mixer, the first mixer configured to mix the operating signal witha first signal to generate a transmission signal.
 2. The transmitteraccording to claim 1, wherein the selection signal varies as a functionof time.
 3. The transmitter according to claim 2, further comprising asecond mixer, the second mixer configured to mix an input data signalwith a second signal to generate the first signal.
 4. The transmitteraccording to claim 3, further comprising a signal shaping circuitry, thesignal shaping circuitry configured to generate the second signal byshaping the reference signal.
 5. The transmitter according to claim 4,wherein the input data signal comprises a modulated data signal.
 6. Thetransmitter according to claim 5, wherein the input data signalcomprises a binary phase shift keyed (BPSK) signal.
 7. The transmitteraccording to claim 5, wherein the input data signal comprises aquadrature amplitude modulated (QAM) signal.
 8. The transmitteraccording to claim 5, wherein the input data signal comprises aquadrature phase shift keyed (QPSK) signal.
 9. The transmitter accordingto claim 4, wherein the signal shaping circuitry is configured tofull-wave rectify the reference signal to generate the second signal.10. The transmitter according to claim 9, wherein the reference signalcomprises a sinewave signal.
 11. The transmitter according to claim 4,wherein the signal shaping circuitry is configured to generate aGaussian-shaped signal as the second signal.
 12. The transmitteraccording to claim 4, wherein the signal shaping circuitry comprises afilter.
 13. The transmitter according to claim 2, wherein the selectionsignal varies according to a channel frequency plan.
 14. The transmitteraccording to claim 13, wherein the selection signal further variesaccording to a channel timing plan.
 15. The transmitter according toclaim 1, further comprising a filter, the filter configured to receivethe transmission signal, the filter further configured to generate afiltered transmission signal.
 16. The transmitter according to claim 1,wherein the frequency of the operating signal equals the frequency ofthe reference signal multiplied by an integer number.
 17. Thetransmitter according to claim 1, wherein the frequency of the operatingsignal equals the frequency of the reference signal multiplied by anon-integer number.
 18. A receiver, comprising: a first mixer, the firstmixer configured to mix an input radio-frequency (RF) signal with afirst signal to generate a first mixed signal; a integrator/sampler, theintegrator/sampler configured to receive the first mixed signal and toprovide an output signal; a signal generator, the signal generatorconfigured to provide an operating signal in response to a selectionsignal, wherein the operating signal has a frequency equal to thefrequency of a reference signal, multiplied by a number; and a secondmixer, the second mixer configured to mix the operating signal with atemplate signal to generate the first signal.
 19. The receiver accordingto claim 18, wherein the selection signal varies as a function of time.20. The receiver according to claim 19, further comprising a referencesignal generator, the reference signal generator configured to generatethe reference signal.
 21. The receiver according to claim 20, furthercomprising a template signal generator, the template signal generatorconfigured to provide the template signal.
 22. The receiver according toclaim 21, wherein the template signal generator is further configured toshape the reference signal to generate the template signal.
 23. Thereceiver according to claim 19, wherein the output signal of theintegrator/sampler comprises a signal derived from the first mixedsignal.
 24. The receiver according to claim 23, further comprising acontroller, the controller configured to generate a datum value from theoutput signal of the integrator/sampler.
 25. The receiver according toclaim 24, wherein the input radio-frequency (RF) signal comprises abinary phase shift keyed (BPSK) signal.
 26. The receiver according toclaim 24, wherein the input radio-frequency (RF) signal comprises aquadrature amplitude modulated (QAM) signal.
 27. The receiver accordingto claim 24, wherein the input radio-frequency (RF) signal comprises aquadrature phase shift keyed (QPSK) signal.
 28. The receiver accordingto claim 22, wherein the template signal generator is further configuredto shape the reference signal by full-wave rectifying the referencesignal.
 29. The receiver according to claim 22, wherein the templatesignal generator is further configured to shape the reference signal bygenerating a Gaussian-shaped signal from the reference signal.
 30. Thereceiver according to claim 22, wherein the template signal generator isfurther configured to shape the reference signal by filtering thereference signal.
 31. The receiver according to claim 24, wherein thereference signal generator comprises a phase locked loop (PLL).
 32. Thereceiver according to claim 31, wherein the controller is furtherconfigured to provide a control signal to the phase locked loop.
 33. Thereceiver according to claim 24, wherein the controller is furtherconfigured to provide the selection signal.
 34. The receiver accordingto claim 19, wherein the selection signal varies according to a channelfrequency plan.
 35. The receiver according to claim 34, wherein theselection signal further varies according to a channel timing plan. 36.The receiver according to claim 18, wherein the frequency of theoperating signal equals the frequency of the reference signal multipliedby an integer number.
 37. The receiver according to claim 18, whereinthe frequency of the operating signal equals the frequency of thereference signal multiplied by a non-integer number.